A heat pump interoperation hot water feeding apparatus comprising: a first coolant circulation circuit that circulates a first coolant by a first compressor that compresses the first coolant; a second coolant circulation circuit that circulates a second coolant by a second compressor that compresses the second coolant; a used water circulation circuit that discharges used water that is heat exchanged with one of the first coolant and the second coolant; a cascade heat exchanger, wherein the first and second coolant circulation circuits (III, IV) partially cross each other so that during a room heating operation, the first coolant is primarily condensed by the used water circulation circuit in a first heat exchanger and then heat exchanged with the second coolant to be secondarily condensed in the cascade heat exchanger, and the second coolant is heat exchanged with the first coolant to be evaporated in the cascade heat exchanger; the first heat exchanger arranged over the first coolant circulation circuit, wherein the first heat exchanger primarily condenses the first coolant by allowing the first coolant to be heat exchanged with the used water flowing through the used water circulation circuit during a room heating operation; and a second heat exchanger arranged over the second coolant circulation circuit, wherein the second heat exchanger primarily condenses the second coolant by allowing the second coolant to be heat exchanged with the used water flowing through the used water circulation circuit during a room heating operation, wherein the used water circulation circuit allows the used water to be heat exchanged with both or either of the first coolant and/or the second coolant through both or either of the first heat exchanger and/or the second heat exchanger depending on the target water temperature of the used water, wherein there are means for determining depending on a target water temperature of the used water and optionally on one of an external air temperature and an indoor temperature whether to operate either one of the first coolant circulation circuit and the second coolant circulation circuit or both the first and second coolant circulation circuits (III, IV). a first coolant circulation circuit that circulates a first coolant by a first compressor that compresses the first coolant; a second coolant circulation circuit that circulates a second coolant by a second compressor that compresses the second coolant; a used water circulation circuit that discharges used water that is heat exchanged with one of the first coolant and the second coolant; a cascade heat exchanger, wherein the first and second coolant circulation circuits (III, IV) partially cross each other so that during a room heating operation, the first coolant is primarily condensed by the used water circulation circuit in a first heat exchanger and then heat exchanged with the second coolant to be secondarily condensed in the cascade heat exchanger, and the second coolant is heat exchanged with the first coolant to be evaporated in the cascade heat exchanger; the first heat exchanger arranged over the first coolant circulation circuit, wherein the first heat exchanger primarily condenses the first coolant by allowing the first coolant to be heat exchanged with the used water flowing through the used water circulation circuit during a room heating operation; and a second heat exchanger arranged over the second coolant circulation circuit, wherein the second heat exchanger primarily condenses the second coolant by allowing the second coolant to be heat exchanged with the used water flowing through the used water circulation circuit during a room heating operation, wherein the used water circulation circuit allows the used water to be heat exchanged with both or either of the first coolant and/or the second coolant through both or either of the first heat exchanger and/or the second heat exchanger depending on the target water temperature of the used water, wherein there are means for determining depending on a target water temperature of the used water and optionally on one of an external air temperature and an indoor temperature