PURPOSE: To ensure stable operation and to enable input of operation optimum to each operation mode by a method wherein a valve device the opening of which is regulatable is mounted in a bypass circuit to control an amount of a refrigerant flowing through a refrigerant circuit, and the bypass circuit is coupled to the high pressure side and the low pressure side of a compressor.

CONSTITUTION: A compressor 1, a 4-way valve 2, a solenoid valve V5, a heat exchanger 9 for hot water storage, an expansion valve 10, solenoid valves V4 and V2, a regenerative refrigerant circuit 11, a heat regenerator 13, a solenoid valve V7, and an indoor heat exchanger 3 are intercoupled, in order named, through a piping to form a refrigerant circuit to perform hot storage and regeneration operation. Cooling and heating operation are switched by the 4-way valve 2. A refrigerant in each operation mode is circulated through a refrigerant circuit through control of solenoid valves V1-V7, and an optimum amount of a refrigerant in a refrigerant circuit is widely changed by being influenced by an outdoor and an indoor state when a device is operated classified by an operation mode and effects heat pump operation. Thus, a refrigerant amount control circuit 15 bypassing the high pressure side and the low pressure side of the compressor 1 is mounted, and an expansion valve 16 capable of controlling a refrigerant amount is provided. A refrigerant amount optimum to each operation mode is ensured through control of the expansion valve 16, and during operation classified by an operation mode and heat pump operation, a stable operation state can be produced.