PURPOSE: To easily make centralized control of the illuminance generated by a plurality of illuminating fixtures by providing a dimming device for each illuminating fixture having an inverter circuit, and furnishing circuits for receiving signals from a master unit, interpreting, and emitting appropriate control signals.

CONSTITUTION: On the time division basis, a master unit transmits multiple transmission signals including address data which specifies the dimming device and/or switch part of any of illuminating fixtures, monitors the operating conditions of different parts, and controls the dimming devices according to the operation on the switch parts. In the case of centralized control, ther dimming devices receive signals from the master unit transmitted via a signal line 24 by a signal transmitting/receiving circuit 8. When a signal processing circuit 9 judges that the given address data is identical to the address data inherent in itself, the control data is taken in, and an appropriate control signal is sent via an output circuit 12. A dim signal emitted from the output circuit 12 is controlled in accordance with the room illuminance sensed by an illuminance sensor 6, and the illuminance of the applicable illuminating fixture is adjusted.