PURPOSE: To improve a rush current suppressing characteristic by operating a connector and short-circuiting a rush current suppressing resistor, when the instantaneous value of an AC voltage becomes O volt.

CONSTITUTION: From a moment when a switch 9 is made, a voltage comparator 2 detects the voltage value (AC voltage value) of an AC power source 1 and compares it with a reference voltage. And when the AC voltage value is higher than the reference voltage, it outputs a comparison signal after the passage of a constant time. A voltage detector 3 detects that the instantaneous value of the AC voltage value becomes O volt from the moment when the switch 9 is made likewise, and outputs a detection signal. A connector 5 is operated by the output signal of an AND circuit 6, and short-circuits a rush current suppressing resistor 4 connected in parallel.