PURPOSE: To reduce unnecessary power loss in a voltage lowering resistance by using part or whole of the current of a resistance load applied during the discharge period of a smoothing condenser for maintaining the current flowing through an on-angle control circuit as the power for the control circuit.

CONSTITUTION: To prevent a phase control dimmer 2 from functioning incorrectly, a load resistance 4 is turned on and off at the timing of a waveform (b) including the output voltage waveform V1 (waveform a) of a full wave rectifier 3 and a short overlap time Ta. The timing of the waveform (b) is formed in a control circuit 14 based on the waveform V1 divided with resistances 8 and 9. A signal for driving a transistor 6 is outputted via a resistance 5, a transistor 7, a diode 10, and a resistance 11. Applying the current flowing through the load resistance 4 directly to the power source of the control circuit 14, the current flowing through the load resistance 4 is effectively utilized, and accordingly the currents flowing through resistances 16 and 17 may be reduced. As a result, unnecessary electric power loss is reduced.