A heat pump system comprising: a heat pump circuit formed by sequentially connecting, to one another, a compressing mechanism including a high stage-side compressing mechanism and a low stage-side compressing mechanism, a first expanding device and a heat source-side heat exchanger through at least a pipe, and refrigerant circulating through the heat pump circuit; a control device for controlling operation of the heat pump system; a utilization-side heating medium circuit through which utilization-side heating medium flows; a utilization-side heat exchanger for heat-exchanging between the refrigerant flowing from the high stage-side compressing mechanism to the first expanding device and the utilization-side heating medium flowing through the utilization-side heating medium circuit; an intercooler for heat-exchanging between the refrigerant discharged from the low stage-side compressing mechanism and the utilization-side heating medium flowing through the utilization-side heating medium circuit; and an injection refrigerant circuit in which the refrigerant flowing through the heat pump circuit is branched off from a position between the utilization-side heat exchanger and the first expanding device, the branched refrigerant is decompressed by a second expanding device, thereafter, the refrigerant joins up, with the refrigerant after it flows out from the intercooler, and the joined refrigerant is sucked into the high stage-side compressing mechanism; wherein the utilization-side heat exchanger and the intercooler are connected to each other in series in the utilization-side heating medium circuit, and the control device is configured to adjust decompression amounts of the first expanding device and the second expanding device such that a ratio of the circulation amount of refrigerant on the side of the injection refrigerant circuit with respect to the circulation amount of refrigerant of the heat pump circuit becomes 30% to 60%, whereby a ratio of a heating capacity Q2 in the intercooler with respect to a total of a heating capacity Q1 in the utilization-side heat exchanger and the heating capacity Q2 in the intercooler is 15% to 25%. a heat pump circuit formed by sequentially connecting, to one another, a compressing mechanism including a high stage-side compressing mechanism and a low stage-side compressing mechanism, a first expanding device and a heat source-side heat exchanger through at least a pipe, and refrigerant circulating through the heat pump circuit; a control device for controlling operation of the heat pump system; a utilization-side heating medium circuit through which utilization-side heating medium flows; a utilization-side heat exchanger for heat-exchanging between the refrigerant flowing from the high stage-side compressing mechanism to the first expanding device and the utilization-side heating medium flowing through the utilization-side heating medium circuit; an intercooler for heat-exchanging between the refrigerant discharged from the low stage-side compressing mechanism and the utilization-side heating medium flowing through the utilization-side heating medium circuit; and an injection refrigerant circuit in which the refrigerant flowing through the heat pump circuit is branched off from a position between the utilization-side heat exchanger and the first expanding device, the branched refrigerant is decompressed by a second expanding device, thereafter, the refrigerant joins up, with the refrigerant after it flows out from the intercooler, and the joined refrigerant is sucked into the high stage-side compressing mechanism; wherein the utilization-side heat exchanger and the intercooler are connected to each other in series in the utilization-side heating medium circuit, and the control device is configured to adjust decompression amounts of the first expanding device and the second expanding device such that a ratio of the circulation amount of refrigerant on the side of the injection refrigerant circuit with respect to the circulation amount of refrigerant of the heat pump circuit becomes 30% to 60%, whereby a ratio of a heating capacity Q2 in the intercooler with respect to a total of a heating capacity Q1 in the utilization-side heat exchanger and the heating capacity Q2 in the intercooler is 15% to 25%.