In a heat pump apparatus, switching between high efficiency operation, and high capacity operation, is performed according to the state of the load. A main refrigerant circuit uses an ejector. A first sub-refrigerant circuit connects a portion between a heat exchanger and an ejector to a portion between a gas-liquid separator and a heat exchanger A second sub-refrigerant circuit connects a portion between the heat exchanger and the ejector to an injection pipe of a compressor. When the load is medium, refrigerant is circulated in the main refrigerant circuit to perform an efficient ejector aided operation. When the load is large, a high capacity injection operation is performed by flowing refrigerant to the second sub-refrigerant circuit. When the load is small, a simple bypass operation prevents degradation of efficiency by flowing refrigerant to the first sub-refrigerant circuit.