To reduce key action force by connecting a bolt member protruded/ retracted by a key action and a lock cam coupled with a main body side piece via a link plate, and preventing the lock cam from being directly driven by a key.

When a key is inserted into the keyway of a lock 10 and rotated CCW for unlocking, a cam in a lock box 11 is rotated, a bolt member 15c is retreated against the exciting force of a spring, and the tip section of the bolt member 15c is released from the angular hole of a lock plate 20. The lock plate 20 automatically drops, and the bolt member 15c is kept at the retreated state. When a door body 13 is opened with a hand, a lock cam 27 is rotated around a pin 29, its locking to a piece 30 is released, a link plate 25 and the lock plate 20 are concurrently lowered, and a stopper is forcefully lowered. When the door body 13 is closed, the bolt member 15c and the lock cam 27 can be concurrently locked. A key action can be made lightly.