A heat pump device (100, 100A) comprising: a first refrigerant circuit that makes a first refrigerant circulate therethrough by connecting a first compressor, a heat-source-side heat exchanger, a first expansion device, a first on-off device, and a refrigerant-side passage in a heat exchanger related to heat medium with refrigerant pipes; a first heat medium circuit that makes a first heat medium circulate therethrough by connecting a pump, a use-side heat exchanger, a heat-medium-side passage in the heat exchanger related to heat medium with heat medium pipes; a second refrigerant circuit that makes a second refrigerant circulate therethrough by connecting a second compressor, a first heat exchanger, a second expansion device, and a second heat exchanger with refrigerant pipes; and a second heat medium circuit that makes a second heat medium circulate therethrough, the second heat medium exchanging heat with the second refrigerant via the first heat exchanger, wherein the first compressor and the heat-source-side heat exchanger are included in an outdoor unit, wherein the first expansion device, the first on-off device, the heat exchanger related to heat medium, and the pump are included in a heat medium relay unit, wherein the use-side heat exchanger is included in an indoor unit, wherein the second compressor, the first heat exchanger, the second expansion device, and the second heat exchanger are included in a water heating unit, wherein the first refrigerant circuit and the second refrigerant circuit are connected to each other via the second heat exchanger included in the water heating unit, and the first heat exchanger is capable to heat the second heat medium, wherein a third expansion device is provided at an outlet side for the heat-source-side refrigerant of the second heat exchanger included in the water heating unit, and wherein inflow of the heat-source-side refrigerant toward the water heating unit is controlled based on an opening degree of the third expansion device. a first refrigerant circuit that makes a first refrigerant circulate therethrough by connecting a first compressor, a heat-source-side heat exchanger, a first expansion device, a first on-off device, and a refrigerant-side passage in a heat exchanger related to heat medium with refrigerant pipes; a first heat medium circuit that makes a first heat medium circulate therethrough by connecting a pump, a use-side heat exchanger, a heat-medium-side passage in the heat exchanger related to heat medium with heat medium pipes; a second refrigerant circuit that makes a second refrigerant circulate therethrough by connecting a second compressor, a first heat exchanger, a second expansion device, and a second heat exchanger with refrigerant pipes; and a second heat medium circuit that makes a second heat medium circulate therethrough, the second heat medium exchanging heat with the second refrigerant via the first heat exchanger, wherein the first compressor and the heat-source-side heat exchanger are included in an outdoor unit, wherein the first expansion device, the first on-off device, the heat exchanger related to heat medium, and the pump are included in a heat medium relay unit, wherein the use-side heat exchanger is included in an indoor unit, wherein the second compressor, the first heat exchanger, the second expansion device, and the second heat exchanger are included in a water heating unit, wherein the first refrigerant circuit and the second refrigerant circuit are connected to each other via the second heat exchanger included in the water heating unit, and the first heat exchanger is capable to heat the second heat medium, wherein a third expansion device is provided at an outlet side for the heat-source-side refrigerant of the second heat exchanger included in the water heating unit, and wherein inflow of the heat-source-side refrigerant toward the water heating unit is controlled based on an opening degree of the third expansion device.