To provide a device capable of unlocking a door lock by posterially attaching it to an existing door.

In a door 2 of a style to move forward and backward a door lock 12 having a slide inclined face by operating a door knob 13, the lock is cancelled by sliding a plate 8 along the inclined face of the doorlock 12. Since an existing door 2 has a some gap between the door 2 and the door frame, the plate 8 to be able to enter between them is used. The plate 8 is fixed to the door through sliding parts 4, 9 to mutually fit for sliding, and is driven by a motor having a speed reducer.