PURPOSE: To improve operability by providing a means for moving a bolt pulling means from a driving disk when the bolt is in the withdrawn position and a means for unlocking the bolt when a door is once opened and closed again.

CONSTITUTION: When a bolt 70 is withdrawn by rotating clockwise a knob and driving a pull hook 90 rightward, a scrambling finger-shaped projection 80 moves rearward and rolls over a combination disk 100 until the free end falls into a notch 102. The finger-shaped projection 53 of a rocking lever 50 falls on the shoulder of the bolt 70, and when a hook 90 moves, it pushes an unlocking finger-shaped projection 94 against a spring 98. Subsequently, when a knob is released, the spring 98 rotates the projection 94 clockwise, the projection 94 swivels counterclockwise the hook 90 and leaves the notch 141 of the main driving disk 130, releasing locking. Subsequently, when a door is closed again, a clasp 230 is rotated clockwise, and a spring 235 adjoins the end 57 of a pusher 55. Furthermore, the projection 53 of the lever 50 is released from the stop face 73 of the bolt 70, and the bolt 70 is pushed to the expanded position by a blade spring.