Heat pump apparatus

An air conditioner, which is a heat pump apparatus, includes a refrigerant circuit, a compressor, and a composition adjustment mechanism. The refrigerant circuit circulates a non-azeotropic mixture refrigerant including a first refrigerant and a second refrigerant having a boiling point higher than the first refrigerant. The compressor compresses the non-azeotropic mixture refrigerant. The first refrigerant is a compound represented by a molecular formula having one or more carbon-carbon unsaturated bonds. The composition adjustment mechanism is provided in the refrigerant circuit. The composition adjustment mechanism prevents an increase in the rate of the first refrigerant included in the non-azeotropic mixture refrigerant discharged from the compressor.