PURPOSE: To prevent a power source from being damaged by the burning loss of a resistor for rush current limit on recoverying current, by setting detection reference voltage on recovering current higher than detection reference voltage on momentary interruption.

CONSTITUTION: In an input voltage monitor circuit 19, a feedback circuit with resistor 18 is attached to a comparator 14. Detection reference voltage on momentary interruption is normalized by reference voltage divided by resistors 16, 17, and detection reference voltage on covering current is set at a high voltage value by a feedback action via the resistor 18. The output of the AC input voltage monitor circuit 19 is applied to a voltage control circuit 30 via a delay circuit 20 and a time constant circuit 29, and a DC-DC converter 6 is controlled by the voltage control circuit 30.