PURPOSE: To facilitate unlocking even in the dark and allow children to open and close it.

CONSTITUTION: A lock body 1 comprises a moving member 17 wherein a slit 9 into which a card key 7 is inserted, a plurality of first protrusions 11 protruded in a position situated deep in the slit 9, second protrusions 13 protruded in a position situated deeper than the first protrusions 11, a moving member 17, and an engaging end 15 engageable with a member 3 to be engaged are integrally formed, and a spring 19 to energize the moving member 17 in a direction in which the card key 7 is inserted. By engaging the member 3 to be engaged with the engaging end 15, the lock body 1 and the member 3 to be engaged are locked. By inserting the card key 7, having a protrusion part not coinciding with any first protrusion 11 but coinciding with one of the second protrusions 13, in the slit 9, the second protrusion 13 is pushed. By moving the engaging end 15 along with the pushing of the second protrusion, engagement is released.