To provide an unbreakable lid for covering a water or gas valve in order to temporarily prohibit the use of the valve during which it can be opened only with a key.

A metallic lid 10 having no seam or joint on its top surface and side surfaces capable of fully wrapping a ring-shaped handle 40 of a valve V in the lid can put in or out the handle through the bottom opening of the lid. A hooking jaw 12 projected out inwardly and a corresponding movable latch 13 facing the jaw are provided at the edge of an opening of at the bottom surface. The hooking jaw 12 and the latch 13 cannot separate from the lower side of the handle 40. When the latch 13 is hooked to a lock claw 21 provided at the latch 13 and the lid 10, the latch 13 is locked, by the insertion of the key 45, the lock claw 21 is separated, and the lock is released and opened.