To weld a main body base part and a back cover without exerting influence on the shape and the dimension of outside appearance.

A 1st projecting piece 36 and a 2nd projecting piece 37 are provided near a finder 38 on the back of the main body base part 13. A 1st aperture 40 and a 2nd aperture 41 are provided on the back cover 15. When the cover 15 is assembled in the base part 13, the 1st and the 2nd projecting pieces 36 and 37 respectively pierce through the 1st and the 2nd apertures 40 and 41. The projecting parts of the 1st and the 2nd projecting pieces 36 and 37 are melted to weld and couple the base part 13 and the cover 15 near the finder 38. A tool insertion hole for ultrasonic welding is provided on the bottom face of the base part 13. A tool abutting surface opposed to the back of the base part 13 is provided in the tool insertion hole. Either tool is inserted in the tool insertion hole to abut on the tool abutting surface, and the other tool is ultrasonically welded while abutting on the cover 15. The base part 13 and the cover 15 are welded and coupled near the bottom face of the base part 13.