PURPOSE: To improve capability by a method wherein a refrigerant changing-over three-way valve is connected between a compressor and a four-way changing-over valve, the second outlet is connected to a hot water feeding heat exchanger, one of the two refrigerant gas controlling two-way valves at the outlet side of the heat exchanger is connected to a cold water heat exchanger and the other refrigerant gas controlling two-way valve is connected to an air heat exchanger.

CONSTITUTION: Refrigerant gas from a compressor 1 is sent to a hot water heat exchanger 3 through a three-way valve under a single hot water feeding operation, the fed hot water is heated. The refrigerant gas reaches a check valve 11, a two-way valve 10 and an expansion valve 12, becoming refrigerant gas of low temperature and low pressure. The refrigerant gas passes through an air heat exchanger 7, a four-way changing-over valve 4 and an accumulator 8 and returns to a compressor 1. During a heating operation, the refrigerant gas flows to the three-way valve 2 and the four-way changing-over valve 4, heats the hot water at the cold water heat exchanger 5, thereafter the gas flows through an air heat exchanger 7, the four-way changing-over valve 4 and an accumulator 8 and returns to the compressor 1. Even in the case of single cooling operation and hot water feeding operation, the refrigerant gas is flowed only in the heat exchanger required in each of the operation modes and then capability can be improved by reducing a resistance of the refrigerant gas.