PURPOSE: To prevent a burglar securely by providing a secondary lock operating member for engaging with a latch operating member in the latch position and for restraining a movement of the latch operating member from the latch position to the latch cancelling position.

CONSTITUTION: A latch operating lever 14 is operated to engage 1 latch with a strike 32 and make the latched condition. Next, at the time of closing a door, when a key inserted into a key cylinder 34 is turned extra than the ordinary position by the predetermined angle, a lock switch is turned ON. Next, a secondary lock actuator 44 is operated to project a secondary lock operation rod 50 and hinder the turning of the latch operating lever 14 to the anticlockwise, and restrain a movement from the latch position to the latch cancelling position.