To protect a compressor from anomalies, such as overload, at voltage drop, and reduce the occurrence of compressor lock condition by stopping the operation of the compressor when supply voltage drops lower than a set voltage using a low voltage protecting means, and increasing the voltage set on the low voltage protecting means by a specified value when overvoltage is detected.

The voltage of a power supply 1 transformed by a transformer 10, and rectified and smoothed by a diode bridge, a resistor 11 and a capacitor 12. It is then input to the supply voltage detecting circuit 14 in a control circuit 2. When fed with a signal from an overcurrent detecting circuit 13, a restart voltage changing circuit 15 increases supply voltage that can be restarted relative to the voltage detected at the supply voltage detecting circuit 14, and transmits a changed set voltage to a low voltage protective circuit 16. The low voltage protective circuit 16 controls a start control circuit 17 and turns on/off a power relay 3 based on this set voltage. It stops the operation of a compressor 4 if the voltage of the power supply 1 drops lower than a preset voltage value.