PURPOSE: To permit a key to be exchanged to automatic or usual lock by a method in which a change knob pivotally attached to a case buried in the end of door is turned toward the direction of automatic locking or usual locking.
CONSTITUTION: A projection 21 is formed on the peripheral side of a change knob 14 pivotally attached to the wall of a case 1 and inserted into a hole formed in a change plate 10. When a door is closed by turning the knob 14 to automatic locking, a trigger bolt 7 is retracted and a stopper 24 is turned by a swing plate 27. The projection 25 is separated from a coupler 44, retractor 36 is pushed backwards by a slider 39, and a dead bolt 45 is projected by a cam plate 29. When the door is closed by turning the knob 14 to usual locking, the plate 27 is pressed by the retraction of the bolt 7 but the stopper 24 does not turn and the retractor 36 is not pushed backwards. The bolt 45 can thus be kept in a buried state.