To hold a first case and a second case in an arbitrary opening/closing position, and also facilitate the assembly work thereof.

Cylindrical shafts 25, 26 are set on both the sides of an end face 3a of the upper inside case 3, and a shaft part 28 is put into one of these cylindrical shafts 25 partly projecting from the cylindrical shafts 25, and on the tip end of the projecting shaft part 28, a through hole 31 in an elastic member 30 is put to fix an elastic member 30 thereto, then the elastic member 30 is forcibly inserted in the press insertion part 34 of a bearing part 32 formed on the end face 7a of a lower inside case 7. Accordingly, since only the elastic member 30 fixed on the shaft part of the upper inside case 3 is pressed into the press insertion part 34 of the bearing part 32, fabrication can be simply done without the use of any special jigs. Moreover, by forcibly inserting the elastic member 30 into the press insertion part 34, the elastic member 30 is elastically deformed so as to bring the inner surface of the piercing hole 31 in close contact with the outer peripheral surface of the shaft part 28. By friction forces through the press contact, the upper case 1 and lower case 2 can be held in an arbitrary opening and closing position.