PURPOSE: To allow a slider only to move idly even when an external operating member is rotated indiscreetly, and to prevent the damage of an intermediate member by bringing a clutch lever to an unengaged state to the slider under a keying state.

CONSTITUTION: When an external operating member on the indoor or outdoor side is rotated by a hand under a locking state, in which a latch bolt 2 is energized by a latch spring 21 and projected, a slider 3 is displaced to the rear against a return spring 31 through a cam 4. An unconnected state is brought between the slider 3 and a retractor 5 and an unengaged state is brought to the slider 3 of a clutch lever 6 on the retractor 5, thus resulting in displacement to the rear of the slider 3 only to an idle movement. An electric lock is released in such a manner that electricity is conducted through an electric actuator 7, an actuating lever 8 is rocked in the counterclockwise direction through a plunger 71, and the external operating member is turned and operated during a time when the clutch lever 6 is engaged with the slider 3.