An outdoor unit includes an outdoor unit control circuit, an inverter substrate and a compressor. Periodic communication showing the operating condition of the inverter substrate is set from the inverter substrate to the outdoor unit control circuit. Thus, when the communication is performed normally, the drive of the compressor is changed to a power saving process according to the necessity of the power consumption and the operating condition of the inverter substrate. When the communication is defective, the power-on reset is done to the inverter substrate.