A heat pump apparatus comprising a compressor, four-way valves (21, 22), an outdoor heat exchanger, a first expansion device, a receiver, a second expansion device, a third expansion device, heat exchanger units (3, 4), and an accumulator, which are sequentially connected in series by refrigerant pipes, wherein: the outdoor heat exchanger includes a first part and a second part divided from each other; the four-way valves (21, 22) include a first four-way valve connected to the first part of the outdoor heat exchanger, and a second four-way valve arranged in parallel with the first four-way valve and connected to the second part of the outdoor heat exchanger; the heat exchanger units (3, 4) include a first heat exchanger unit connected to the first four-way valve, and a second heat exchanger unit connected to the second four-way valve; the first four-way valve includes a first port connected to an outlet side of the compressor, a second port connected to the first part of the outdoor heat exchanger, a third port connected to the accumulator, and a fourth port connected to the first heat exchanger unit; the second four-way valve includes a first port connected to the outlet side of the compressor, a second port connected to the second part of the outdoor heat exchanger, a third port connected to the accumulator, and a fourth port connected to the second heat exchanger unit; the heat pump apparatus further comprises a control device to control the first and second four-way valves (21, 22); and when the first port and the second port of the first four-way valve are connected and the third port and the fourth port of the first four-way valve are connected and the first port and the fourth port of the second four-way valve are connected by the control device, the refrigerant sequentially flows to the compressor, the first and second four-way valves (21, 22), the first part of the outdoor heat exchanger and the second heat exchanger unit, the first and third expansion devices (24, 28), the receiver, the second expansion device, the first heat exchanger unit, the first four-way valve, the accumulator, and the compressor. the outdoor heat exchanger includes a first part and a second part divided from each other; the four-way valves (21, 22) include a first four-way valve connected to the first part of the outdoor heat exchanger, and a second four-way valve arranged in parallel with the first four-way valve and connected to the second part of the outdoor heat exchanger; the heat exchanger units (3, 4) include a first heat exchanger unit connected to the first four-way valve, and a second heat exchanger unit connected to the second four-way valve; the first four-way valve includes a first port connected to an outlet side of the compressor, a second port connected to the first part of the outdoor heat exchanger, a third port connected to the accumulator, and a fourth port connected to the first heat exchanger unit; the second four-way valve includes a first port connected to the outlet side of the compressor, a second port connected to the second part of the outdoor heat exchanger, a third port connected to the accumulator, and a fourth port connected to the second heat exchanger unit; the heat pump apparatus further comprises a control device to control the first and second four-way valves (21, 22); and when the first port and the second port of the first four-way valve are connected and the third port and the fourth port of the first four-way valve are connected and the first port and the fourth port of the second four-way valve are connected by the control device, the refrigerant sequentially flows to the compressor, the first and second four-way valves (21, 22), the first part of the outdoor heat exchanger and the second heat exchanger unit, the first and third expansion devices (24, 28), the receiver, the second expansion device, the first heat exchanger unit, the first four-way valve, the accumulator, and the compressor.