A heat pump system comprising: a main refrigerant circuit formed by sequentially connecting, through a pipe, a compression mechanism composed of a compression rotation element (11a, 11b), a usage-side heat exchanger for heating usage-side heat medium by refrigerant which is discharged from the compression rotation element (11a, 11b) and which exceeds critical pressure, an intermediate heat exchanger, a first expansion device, and a heat source-side heat exchanger; a bypass refrigerant circuit branched off from the pipe between the usage-side heat exchanger and the first expansion device, in which branched refrigerant is decompressed by a second expansion device and thereafter, heat of the refrigerant is exchanged with that of the refrigerant flowing through the main refrigerant circuit by the intermediate heat exchanger, and the refrigerant joins up with the refrigerant which is in middle of a compression operation of the compression rotation element (11a, 11b); and a control device, a heat medium inlet temperature thermistor for detecting the temperature of the usage-side heat medium which flows into the usage-side heat exchanger, a discharge temperature thermistor which detects temperature of the refrigerant discharged from the compressing rotation element (11a, 11b), wherein when temperature of the usage-side heat medium which flows into the usage-side heat exchanger rises, the control device controls a valve opening of at least the second expansion device, and increases a ratio of an amount of the refrigerant which flows through the bypass refrigerant circuit to an amount of the refrigerant which flows on a side of the main refrigerant circuit of the intermediate heat exchanger, wherein when detected temperature which is detected by the heat medium inlet temperature thermistor rises, the control device operates to increase the valve opening of the second expansion device and operates to reduce a valve opening of the first expansion device, and wherein the control device brings the temperature detected by the discharge temperature thermistor close to a target value by adjusting the valve opening of the first expansion device and the valve opening of the second expansion device. a main refrigerant circuit formed by sequentially connecting, through a pipe, a compression mechanism composed of a compression rotation element (11a, 11b), a usage-side heat exchanger for heating usage-side heat medium by refrigerant which is discharged from the compression rotation element (11a, 11b) and which exceeds critical pressure, an intermediate heat exchanger, a first expansion device, and a heat source-side heat exchanger; a bypass refrigerant circuit branched off from the pipe between the usage-side heat exchanger and the first expansion device, in which branched refrigerant is decompressed by a second expansion device and thereafter, heat of the refrigerant is exchanged with that of the refrigerant flowing through the main refrigerant circuit by the intermediate heat exchanger, and the refrigerant joins up with the refrigerant which is in middle of a compression operation of the compression rotation element (11a, 11b); and a control device, a heat medium inlet temperature thermistor for detecting the temperature of the usage-side heat medium which flows into the usage-side heat exchanger, a discharge temperature thermistor which detects temperature of the refrigerant discharged from the compressing rotation element (11a, 11b), wherein when temperature of the usage-side heat medium which flows into the usage-side heat exchanger rises, the control device controls a valve opening of at least the second expansion device, and increases a ratio of an amount of the refrigerant which flows through the bypass refrigerant circuit to an amount of the refrigerant which flows on a side of the main refrigerant circuit of the intermediate heat exchanger, wherein when detected temperature which is detected by the heat medium inlet temperature thermistor rises, the control device operates to increase the valve opening of the second expansion device and operates to reduce a valve opening of the first expansion device, and wherein the control device brings the temperature detected by the discharge temperature thermistor close to a target value by adjusting the valve opening of the first expansion device and the valve opening of the second expansion device. wherein when temperature of the usage-side heat medium which flows into the usage-side heat exchanger rises, the control device controls a valve opening of at least the second expansion device, and increases a ratio of an amount of the refrigerant which flows through the bypass refrigerant circuit to an amount of the refrigerant which flows on a side of the main refrigerant circuit of the intermediate heat exchanger, wherein when detected temperature which is detected by the heat medium inlet temperature thermistor rises, the control device operates to increase the valve opening of the second expansion device and operates to reduce a valve opening of the first expansion device, and wherein the control device brings the temperature detected by the discharge temperature thermistor close to a target value by adjusting the valve opening of the first expansion device and the valve opening of the second expansion device.