PURPOSE: To readily remove a screw for mounting a case body and to prevent it from being lost when attaching or detaching the case body by temporarily fastening the screw to the body through a plate continually.

CONSTITUTION: A mounting plate 11a for fastening the end of a case body 11 is fastened through a plate 14 to a base 13 with a 11c inside with respect to a case cover 11b and a hole 11d outside, and a slit 11e is formed at the lower end of the cover 11b. The screw 12a is provided with a thread portion 12c of a thread length L which is shorter than the depth of the hole 11d and the thread portion 12c is freely engaged with the hole 11d. The plate 14 has a thickness capable of passing the slit 11e and is provided with a locking hole 14a locked at a projection 11c and a through hole 14b at a position corresponding to the hole 11d. The thread ridges 12c of the screw 12 are in contact with the plate 14 to prevent the screw from falling off. Consequently, when the screw 12 is removed form the thread portion 13a of the base 13 so as to dismount the cover 11b, the screw 12 will not fall off.