PURPOSE: To eliminate the need for a digital adjustment without using a key and enable even a visually handicapped personnel to lock and unlock this key by depressing a pushbutton switch under a dark environment.

CONSTITUTION: A main body vessel 1 is divided into a plurality of small segments by means of partition boards 2 where a combination of a gear 4 having a disk 3 and a magnet A and a sear holding cylinder 5 are inserted into a shaft and mounted in the vertical direction in each small segment respectively. A locking rod 11 having a projection 12 close to the gear 4 is mounted in such a fashion that it may penetrate each partition board 2 in the vertical direction. A magnet B, a gear stopper 17, a shaft B19 having a control arm 18 and a feed tooth claw 15 which makes a reciprocating motion by means of a pushbutton switch 16 are mounted on the outer peripheral area of the gear 4. A reset rod 21 is mounted in contact with the gear stopper 17 and the end of the rod is placed outside in the main body vessel 1.