To improve reliability and comfortability of a system by flowing a flow amount of a refrigerant optimum to a heat-exchanger operating as an evaporator during starting of a compressor or after completion of reverse cycle defrosting operation.

An evaporative temperature computing means estimates an optimum evaporative temperature after a lapse of a given time starting from a present time based on the suction temperatures of an air-cooled heat-exchanger 3 on the heat source side and an air-cooled heat-exchanger 5 on the utilization side during starting of a compressor 1 and a control means performs control of the opening of a motor-driven expansion valve 4 in a manner to reach a target value in a given time with an evaporative temperature determined by the evaporative temperature computing means forming a target value, the two means being annexed. During starting of the compressor 1 or after completion of a reverse cycle defrosting operation, an optimum evaporative temperature after a lapse of a given time starting from a time when it is estimated based on the intake air temperature forms a target value, and the opening of the motor-driven expansion valve 4 is controlled in a manner to reach the target value in the given time.