PURPOSE: To replace a lamp without removing a lamp cover.

CONSTITUTION: When a push button member 10 is moved in the direction of a fixing member 8, a locking hole of a moving member 12 is moved in the direction of unlocking the locking with a locking part of a locking member 15, and the lower edge of a safety spring 14 is moved in the direction of locking with a tongue-shaped part of the locking member 15. The lock of the locking part of the locking member 15 with the locking hole of the moving member 12 is unlocked. Although a lamp cover 5 is due to fall down by unlocking, since the tongue-shaped part of the locking member 15 is locked with the safety spring 14, the lamp cover 5 is caught when falling by the safety spring 14 through the tongue-shaped part and does not fall down.