There are provided a water-refrigerant heat exchanger 30 for exchanging heat between refrigerant discharged from a compressor 21 and engine-cooling water circulating an engine-cooling water circuit 10, prior to being fed into the radiator 22, and a bypass 25 for guiding the refrigerant prior to being fed into the evaporator 24 to the water-coolant heat exchanger 30 while bypassing the evaporator 24 and the compressor 21. When it is desired to accelerate the warming-up of the engine 11, the bypass 25 is closed to operate the compressor 21 to heat the engine-cooling water by high-pressure refrigerant, and when it is desired to complement the capacity of the radiator 12, the bypass 25 is open to guide the liquid-phase refrigerant to the water-refrigerant heat exchanger 30 to effectively cool the refrigerant by using the phase change of the refrigerant.