In a lock mechanism (10), a second member rotatably attached to a first member is secured to the first member. The lock mechanism has a lock pin (11), a lock member (12) that moves according to the advancement of the lock pin, and a first urging member (18A, 18B) that urges the lock member. The lock member has a cam groove (22, 24) into which the lock pin advances with the rotational action of the second member. The cam groove has a locking part (23) that locks the lock pin when the second member has moved to a position of being secured by the first member, and unlocks the lock pin by the locked lock pin being pressed in. The direction in which the lock member moves is set to a direction differing from the direction in which the lock pin enters the cam groove.