A heat pump apparatus comprising: a heat source device configured to cool or heat a refrigerant; a first use device configured to cool a first fluid by utilizing the refrigerant cooled by the heat source device; a second use device configured to heat a second fluid by utilizing the refrigerant heated by the heat source device; and a controller configured to cause, when there is an operation request for one of the first use device and the second use device, even when there is no operation request for the other, both the one and the other to operate if the other satisfies a certain condition, and is configured to cause the first use device and the second use device to perform a waste heat recovery operation, in which the second use device is configured to heat the second fluid by utilizing a refrigerant heated by cooling the first fluid in the first use device and in which the first use device is configured to cool the first fluid by utilizing a refrigerant cooled by heating the second fluid in the second use device, characterised in that the controller is configured to determine that there is an operation request for the second use device if a temperature of the second fluid is less than or equal to a first heating temperature set by a user, and determine that, when there is an operation request for the first use device, even when the temperature of the second fluid is higher than the first heating temperature and there is no operation request for the second use device, the second use device satisfies the certain condition if the temperature of the second fluid is less than or equal to a preset second heating temperature higher than the first heating temperature, and is configured to cause both the first use device and the second use device to operate so that the waste heat recovery operation is performed by the first use device and the second use device. a heat source device configured to cool or heat a refrigerant; a first use device configured to cool a first fluid by utilizing the refrigerant cooled by the heat source device; a second use device configured to heat a second fluid by utilizing the refrigerant heated by the heat source device; and a controller configured to cause, when there is an operation request for one of the first use device and the second use device, even when there is no operation request for the other, both the one and the other to operate if the other satisfies a certain condition, and is configured to cause the first use device and the second use device to perform a waste heat recovery operation, in which the second use device is configured to heat the second fluid by utilizing a refrigerant heated by cooling the first fluid in the first use device and in which the first use device is configured to cool the first fluid by utilizing a refrigerant cooled by heating the second fluid in the second use device, characterised in that the controller is configured to determine that there is an operation request for the second use device if a temperature of the second fluid is less than or equal to a first heating temperature set by a user, and determine that, when there is an operation request for the first use device, even when the temperature of the second fluid is higher than the first heating temperature and there is no operation request for the second use device, the second use device satisfies the certain condition if the temperature of the second fluid is less than or equal to a preset second heating temperature higher than the first heating temperature, and is configured to cause both the first use device and the second use device to operate so that the waste heat recovery operation is performed by the first use device and the second use device.