PURPOSE: To bring locking into a reliable state and to simplify a structure and a mechanism by a method wherein a photo sensor is arranged at the inside of a safe door having an electrically operated locking device, and when a door is closed and the inside is rendered dark, a control device is worked to perform locking.

CONSTITUTION: A photo sensor 18 is arranged at an electrically operated locking device 14 arranged at the inside of a door 12 for a safe 10. Further, a control device 16 for the locking device 14 is arranged at the outside of the door 12 and connected through an electric wire L4. When the door 12 is closed and darkness is detected by the photo sensor 18, the control device 16 is actuated to effect locking. In a case of locking, when the control device 16 is operated to effect opening, the sensor 18 senses brightness, and the locking device is not operated. Further, by operating the control unit 16, a lock is locked and unlocked. This constitution performs reliable locking.