To provide a digital auxiliary lock not requiring a key and allowing the user to set an unlocking number particular to the lock possessed by the user, for solving the problem that the user has to possess and control two keys, that is, a key for a main lock and a key for an auxiliary lock when the auxiliary lock is installed on a double sliding door.

The auxiliary lock comprises a strike and a locking part, which are provided in the overlapping part of the double sliding door; the strike comprises a mounting part and a latching part; the locking part comprises a stopper part and a digital operation part; the digital operation part has a plurality of buttons; the stopper part can be hooked and unhooked to/from the latching part by operating an arbitrary one of the buttons; and the selection of the arbitrary button can be freely changed.