PURPOSE: To sufficiently improve the safety of a lock device and prevent a keyhole from being meddled.

CONSTITUTION: A lock protector fitted to cover the keyhole 4 of a lock and protecting the keyhole 4 is constituted of a protector main body 1 fitted to cover the keyhole 4 and a magnet key 2, and the protector main body 1 has a cover main body 10 provided with through holes serving as windows 11b, 12b exposing the keyhole 4 and a door 13 slid to open or close the through holes. The door 13 has a magnet 14 on its back face, and the magnet 14 is protruded on the back side in the normal state and withdrawn when the magnet key 2 is brought into contact with the surface of the door 13. A projection 12a is provided at the back side portion of the door 13 of the cover main body 10, the projection 12a is hooked on the magnet 14 in the protruded state, and it is not hooked on the magnet 14 in the withdrawn state. The door 13 can not be slid when the magnet 14 is hooked on the projection 12a.