PURPOSE: To improve energy-saving and antitheft control by installing a locking device in which a tenant key insertion and extraction operation is linked up with a power interrupting and making operation of electric equipment, and controlling it after its detection at a time when a tenant key is left intact.

CONSTITUTION: At the time of entering, when a magnetic card 4 is inserted both magnetic card readers 3, 12 of a central processing unit 5a checks both discrimination and registered data, thereby unlocking a side door 2 and a door of a key box 7. Next, an entrant extracts a tenant key from a locking device 13, and with a contact 18 turned ON, the central processing unit 5a energizes an air conditioner 20a, a lighting system 20b, or the like with current. At the time of leaving, the entrant inserts the magnetic card 4 into the magnetic card reader 12, opening the door of the key box 7, and inserts the tenant key into the locking device 13. In addition, the contact 18 is turned to OFF, and the central processing unit 5a opens a switch at the power side, stopping a flow of electricity. When the key is left intact in a key storage, for example, the tenant key is not yet inserted into the locking device 13 and so on, a contact 16a is turned to ON, operating a voice generator 17, thus a voice alarm is emitted.