To achieve an air-conditioning mode, a heating mode and a dehumidification heating mode, by using a simple cycle configuration, concerning a heat pump cycle for composing a cycle of gas injection.

In the heat pump cycle for composing the cycle of gas injection, both of a high stage side decompression means (high stage side expansion valve 13) and low stage side decompression means (low pressure side on-off valve 16b, low stage side fixed throttle 17, and fixed throttle detouring path 18) can be set by a throttled state and a fully opened state. This arrangement achieves the air-conditioning, heating and dehumidification heating modes by the simple configuration, without separately arranging a refrigerant flow path from a compressor 11 to an outdoor heat exchanger 20 according to the operation mode of an air conditioner.