PURPOSE: To improve operability by providing a cam groove engaging with a lock body at closing a shutter on the cam plate of a lock device of which the latch is automatically operated by a spring so as to lock, and holding the cam plate in the unlock position at releasing.

CONSTITUTION: A cam groove 11b is provided on a cam plate 11 combined with a latch always energized, and when the releasing operation is performed by a lock lever, the cam plate 11 is rotated and a lock body 17 is engaged with the cam groove 11b, and hence unlock condition (state shown in the figure) is held. When a shutter is closed, engagement of the lock body 17 is disengaged, the cam plate 11 is reversely rotated so as to be locked. Hereby, operability of the shutter can be improved.