A heat pump apparatus comprising: a main refrigerant circuit, through which refrigerant circulates, configured by connecting a discharge side of a compressor and a first heat exchanger by piping, the first heat exchanger and a first inlet of an ejector by piping, an outlet of the ejector and an inlet of a gas-liquid separator by piping, a gas side outlet of the gas-liquid separator and a suction side of the compressor by piping, a liquid side outlet of the gas-liquid separator and a second heat exchanger by piping, and the second heat exchanger and a second inlet of the ejector by piping; a first sub-refrigerant circuit configured by connecting by piping a first connection point between the first heat exchanger and the first inlet of the ejector in the main refrigerant circuit to a second connection point between the liquid side outlet of the gas-liquid separator and the second heat exchanger in the main refrigerant circuit, and being provided with a first expansion mechanism in the middle of the piping; characterized by a second sub-refrigerant circuit that makes a part of refrigerant flowing through a third connection point between the first heat exchanger and the first inlet of the ejector in the main refrigerant circuit bypass the ejector so as to flow into the compressor, and is provided in its middle with a second expansion mechanism; and a third heat exchanger that performs heat exchange between refrigerant flowing between the first connection point and the first expansion mechanism in the first sub-refrigerant circuit and refrigerant after passing through the second expansion mechanism in the second sub-refrigerant circuit; a control valve that controls an amount of refrigerant which has flowed out of the first heat exchanger and is to be flowed into the first inlet of the ejector; and a control unit that controls an opening degree of the control valve, an opening degree of the first expansion mechanism, and an opening degree of the second expansion mechanism, according to a required load being a heat amount necessary for making a temperature of fluid, which is heat-exchanged with refrigerant flowing through the first heat exchanger, be a predetermined temperature. a main refrigerant circuit, through which refrigerant circulates, configured by connecting a discharge side of a compressor and a first heat exchanger by piping, the first heat exchanger and a first inlet of an ejector by piping, an outlet of the ejector and an inlet of a gas-liquid separator by piping, a gas side outlet of the gas-liquid separator and a suction side of the compressor by piping, a liquid side outlet of the gas-liquid separator and a second heat exchanger by piping, and the second heat exchanger and a second inlet of the ejector by piping; a first sub-refrigerant circuit configured by connecting by piping a first connection point between the first heat exchanger and the first inlet of the ejector in the main refrigerant circuit to a second connection point between the liquid side outlet of the gas-liquid separator and the second heat exchanger in the main refrigerant circuit, and being provided with a first expansion mechanism in the middle of the piping; a second sub-refrigerant circuit that makes a part of refrigerant flowing through a third connection point between the first heat exchanger and the first inlet of the ejector in the main refrigerant circuit bypass the ejector so as to flow into the compressor, and is provided in its middle with a second expansion mechanism; and a third heat exchanger that performs heat exchange between refrigerant flowing between the first connection point and the first expansion mechanism in the first sub-refrigerant circuit and refrigerant after passing through the second expansion mechanism in the second sub-refrigerant circuit; a control valve that controls an amount of refrigerant which has flowed out of the first heat exchanger and is to be flowed into the first inlet of the ejector; and a control unit that controls an opening degree of the control valve, an opening degree of the first expansion mechanism, and an opening degree of the second expansion mechanism, according to a required load being a heat amount necessary for making a temperature of fluid, which is heat-exchanged with refrigerant flowing through the first heat exchanger, be a predetermined temperature.