To detect correctly an abnormal condition of a heater of a compressor crankcase at low cost.

This device 40 includes a crankcase heater 41, a resistor 42, a photocoupler 43, and a controller 13. The resistor 42 is connected in series to a heater 41 of a compressor crankcase for heating a compressor body. The photocoupler 43 determines whether voltage is placed upon energization on the resistor of the crank heater. A controller 13 detects a normal/abnormal condition of the crank case heater based on presence/absence of pulse waveform signals output from the photocoupler 43.