A heat pump water heater outdoor unit, in which a compressor, a water heat exchanger for heat exchange between water and a refrigerant, a first decompression device, and an air heat exchanger for exchange between air and the refrigerant are connected with piping, to supply heat absorbed from the air by the refrigerant flowing through the air heat exchanger to the water flowing through the water heat exchanger by the refrigerant flowing through the water heat exchanger, comprising: a first internal heat exchanger provided between the water heat exchanger and the first decompression device and used for heat exchange between a refrigerant flowing between the water heat exchanger and the first decompression device and a refrigerant flowing between the air heat exchanger and the compressor; an injection circuit branching off at a point between the first internal heat exchanger and the first decompression device to inject the refrigerant into the compressor through a second decompression device; a second internal heat exchanger for heat exchange between the refrigerant flowing between the first internal heat exchanger and the first decompression device and the refrigerant flowing between the second decompression device and the compressor in the injection circuit; an ambient temperature sensor for detecting an ambient temperature; and an inflow water temperature sensor for detecting a temperature of the water, namely an inflow water temperature, flowing into the water heat exchanger, wherein the second decompression device corresponds to an expansion valve, characterized in that when at least one of the following conditions a) when the ambient temperature becomes lower than a first predetermined temperature and b) when the inflow water temperature becomes larger than a second predetermined temperature, is satisfied, injection control by the second decompression device is started, wherein a refrigerant superheating degree at the discharge port of the compressor is compared with a target value to determine whether to change the opening degree of the second decompression device. a first internal heat exchanger provided between the water heat exchanger and the first decompression device and used for heat exchange between a refrigerant flowing between the water heat exchanger and the first decompression device and a refrigerant flowing between the air heat exchanger and the compressor; an injection circuit branching off at a point between the first internal heat exchanger and the first decompression device to inject the refrigerant into the compressor through a second decompression device; a second internal heat exchanger for heat exchange between the refrigerant flowing between the first internal heat exchanger and the first decompression device and the refrigerant flowing between the second decompression device and the compressor in the injection circuit; an ambient temperature sensor for detecting an ambient temperature; and an inflow water temperature sensor for detecting a temperature of the water, namely an inflow water temperature, flowing into the water heat exchanger, wherein the second decompression device corresponds to an expansion valve, characterized in that when at least one of the following conditions a) when the ambient temperature becomes lower than a first predetermined temperature and b) when the inflow water temperature becomes larger than a second predetermined temperature, is satisfied, injection control by the second decompression device is started, wherein a refrigerant superheating degree at the discharge port of the compressor is compared with a target value to determine whether to change the opening degree of the second decompression device.