PURPOSE: To enable locking or unlocking not to be performed except for a fixed time by setting a liquid crystal shutter to be driven to be controlled to shield light with a control section only for a specified time, in front of a light receiving section set on an opening or closing member, to covert the light receiving surface of the light receiving section.

CONSTITUTION: When a liquid crystal shutter 15 is set in a light receiving state, then light signal irradiated from a light emitting section 11 is transmitted through the shutter 15 and reaches the light receiving surface of a light receiving section 12. At the light receiving section 12, the output of electric signal is directed to a control section 14, and at the control section 14, an electronic lock 13 is locked or unlocked. After that, from e light emitting section 11, the output of timer setting signal including locking signal and unlocking time for setting a time for setting the shutter 15 in a light shielding state is generated. Then, the set signal is converted to the electric signal at the light receiving section 12 and the input to the control section 14 is provided, and at the control section 14, the electronic lock 13 is locked, and the shutter 15 is driven to be controlled in the light shielding state. Besides, when the unlocking time is set, then unlocking is performed at the control section 14, and the shutter 15 is set in a light transmitting state.