PURPOSE: To discriminate whether or not usage by a copy key is enabled easily, and to discriminate a key without mounting a special part on the key by registering a key number permitting the release of an electric lock, reading the number of the key inserted into a key inserting hole and collating the number of the key with the registered number.

CONSTITUTION: A key 1 permitting the release of an electric lock is inserted into a key inserting hole 2 in a registration mode 3. The number N of the inserted key is read 6. The key number N is registered previously as a registered key number. When the key 1 is inserted into the key inserting hole 2 for releasing the electric lock, light is emitted to the grip section 1a of the key 1 from a light source 5, and the key number N is read optically. The number N is stored temporarily at that time 9. The stored number N is compared with a registered number data 11a. When contents coincide, a key number signal S5 as an ID and decision result signals S6, S7 are output, and the lock is released. Accordingly, the easy release of the electric lock by a copy key can be prevented.