A heat pump system (1, 101, 201) comprising: a refrigerant circuit (20, 120) configured so that a usage unit (4a, 4b, 8a, 8b, 104a, 104b) having a usage-side expansion valve (42a, 42b, 82a, 82b) and a usage-side heat exchanger (41a, 41b, 81a, 81b) is connected to a heat source unit having a compressor for compressing a refrigerant; a heat-source-side heat exchanger; a heat-source-side expansion valve; and an accumulator connected to an intake of said compressor; and a controller (1a, 101a, 201a) for performing a heating operation for causing said usage-side heat exchanger to function as a refrigerant radiator and for controlling said usage-side expansion valve so that, during said heating operation, a degree of subcooling of the outlet refrigerant, which is the degree of subcooling of the refrigerant in an outlet of said usage-side heat exchanger, is equal to a predetermined target degree of subcooling of the outlet refrigerant; characterised in that said controller performs refrigerant recovery control for controlling said heat-source-side expansion valve so that the degree of superheat of the outlet refrigerant, which is the degree of superheat of the refrigerant in an outlet of said heat-source-side heat exchanger functioning as a refrigerant evaporator, is equal to a predetermined target degree of superheat of the outlet refrigerant, for changing said target degree of superheat of the outlet refrigerant so that the refrigerant in the outlet of said heat-source-side heat exchanger is wet when said usage-side expansion valve is opened to be greater than a predetermined opening degree for the start of refrigerant recovery, and for cancelling the change in said target degree of superheat of the outlet refrigerant when said usage-side expansion valve is closed to be smaller than a predetermined opening degree for the end of refrigerant recovery in the state in which said target degree of superheat of the outlet refrigerant is changed. a refrigerant circuit (20, 120) configured so that a usage unit (4a, 4b, 8a, 8b, 104a, 104b) having a usage-side expansion valve (42a, 42b, 82a, 82b) and a usage-side heat exchanger (41a, 41b, 81a, 81b) is connected to a heat source unit having a compressor for compressing a refrigerant; a heat-source-side heat exchanger; a heat-source-side expansion valve; and an accumulator connected to an intake of said compressor; and a controller (1a, 101a, 201a) for performing a heating operation for causing said usage-side heat exchanger to function as a refrigerant radiator and for controlling said usage-side expansion valve so that, during said heating operation, a degree of subcooling of the outlet refrigerant, which is the degree of subcooling of the refrigerant in an outlet of said usage-side heat exchanger, is equal to a predetermined target degree of subcooling of the outlet refrigerant; characterised in that said controller performs refrigerant recovery control for controlling said heat-source-side expansion valve so that the degree of superheat of the outlet refrigerant, which is the degree of superheat of the refrigerant in an outlet of said heat-source-side heat exchanger functioning as a refrigerant evaporator, is equal to a predetermined target degree of superheat of the outlet refrigerant, for changing said target degree of superheat of the outlet refrigerant so that the refrigerant in the outlet of said heat-source-side heat exchanger is wet when said usage-side expansion valve is opened to be greater than a predetermined opening degree for the start of refrigerant recovery, and for cancelling the change in said target degree of superheat of the outlet refrigerant when said usage-side expansion valve is closed to be smaller than a predetermined opening degree for the end of refrigerant recovery in the state in which said target degree of superheat of the outlet refrigerant is changed.