To surely attach a decorative sheet and to unnecessitate work such as selection and reforming of warp and management by providing an almost U-shaped slit on an adhered plane of a front case surface, making the plate thickness of a part that is surrounded by the sit thinner than the other parts and fixing the decorative sheet on the part with an adhesive sheet.

If both of the surfaces to be stuck are hard, the decorative sheet makes oxly partial contact with an adhesive sheet because the surfaces do not fit each other. In such a case, a slit 4 is provided on an adhered plane 3 of a front case surface 2 in an almost U-shaped way, and an adhesive sheet 6 is provided on a thin-walled part 5 that is surrounded by the slit 4. The plate thickness of the part 5 is thinner by 30 to 50% than the other parts. When the decorative sheet is attached to the case 2 that is formed in this way, the part 5 easily becomes familiar with the decorative sheet because the part is weak in strength, the full surface of the sheet 6 is brought into contact and it is prevented from peeling off. Further, the slit 4, the part 5 and the sheet 6 can be located at any part of the plane 3. Also, the more they are, the larger the effect is.