Key Financial Data Of Reporting Company
| Concept | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | 2024-01-01 to 2024-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | 2022-01-01 to 2022-12-31 | As at 2022-12-31 | As at 2021-12-31 | 2021-01-01 to 2021-12-31 | 2020-01-01 to 2020-12-31 | As at 2020-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Key financial data of reporting company | |||||||||||||||
| Business results of reporting company | |||||||||||||||
| Net sales | — | — | — | — | — | — | 
                                                3,072,417,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,640,002,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,955,470,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,416,536,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,458,957,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Ordinary profit (loss) | — | — | — | — | — | — | 
                                                122,937,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                533,438,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                381,371,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                153,686,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -206,787,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Profit (loss) | — | — | — | — | — | — | 
                                                50,671,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                363,695,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                247,541,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                114,200,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -173,204,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Equity in earnings (losses) of affiliates if equity method is applied | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Share capital | 
                                                817,533,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                807,609,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                787,529,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                782,671,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                782,671,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Total number of issued shares | 
                                                5,597,700
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                5,503,600
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | 
                                                5,320,700
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
                                                5,291,400
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | — | — | 
                                                5,291,400
                                                
                                                    
                                                        xbrli:shares
                                                    
                                                
                                             | 
| Net assets | 
                                                2,901,740,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                2,861,174,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                2,457,320,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,200,061,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,085,861,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Total assets | 
                                                4,701,386,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                4,980,604,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                4,332,013,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,808,237,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,784,063,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Net assets per share | 
                                                524.30
                                                
                                             | — | — | — | — | — | — | — | 
                                                519.90
                                                
                                             | — | 
                                                461.87
                                                
                                             | 
                                                415.80
                                                
                                             | — | — | 
                                                394.22
                                                
                                             | 
| Dividend paid per share | — | — | — | — | — | — |  |  | — |  | — | — |  |  | — | 
| Interim dividend paid per share | — | — | — | — | — | — |  |  | — |  | — | — |  |  | — | 
| Basic earnings (loss) per share | — | — | — | — | — | — | 
                                                9.08
                                                
                                             | 
                                                67.87
                                                
                                             | — | 
                                                46.66
                                                
                                             | — | — | 
                                                21.58
                                                
                                             | 
                                                -32.75
                                                
                                             | — | 
| Diluted earnings per share | — | — | — | — | — | — | 
                                                9.03
                                                
                                             | 
                                                65.29
                                                
                                             | — | 
                                                44.66
                                                
                                             | — | — | 
                                                20.66
                                                
                                             |  | — | 
| Equity-to-asset ratio | 
                                                0.617
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                0.574
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.567
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.578
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.551
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Rate of return on equity | — | — | — | — | — | — | 
                                                0.018
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.137
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.106
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.053
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Price-earnings ratio | — | — | — | — | — | — | 
                                                48.6
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                17.5
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                14.9
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                21.7
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Payout ratio | — | — | — | — | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) operating activities | — | — | — | — | — | — | 
                                                529,055,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                389,555,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                600,410,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                456,368,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -28,803,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) investing activities | — | — | — | — | — | — | 
                                                -212,097,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -717,953,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -629,120,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -111,689,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -249,339,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) financing activities | — | — | — | — | — | — | 
                                                -200,489,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                325,079,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                29,009,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -260,489,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                201,675,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Cash and cash equivalents | 
                                                419,712,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                303,243,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                306,561,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                306,261,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                222,072,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Number of employees | 
                                                142
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                21
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                97
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                16
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                121
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                148
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                129
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                128
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                140
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Average number of temporary employees | 
                                                27
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                3
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                16
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                8
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                24
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                29
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                30
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                16
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                16
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Total shareholder return | 
                                                0.395
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                1.066
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.620
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                0.420
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.685
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
| Total return on share price index | 
                                                1.618
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                1.375
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                1.099
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | 
                                                1.157
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                1.048
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             |