A hot water supply device associated with a heat pump and using the heat pump to perform a hot water supply operation, the hot water supply device comprising: a cascade heat pump, including a first refrigerant circulation part that circulates a first refrigerant including a first compressor, a cascade heat exchanger in which heat is exchanged between the first refrigerant and a second refrigerant, a first expander, a first refrigerant-water heat exchanger configured such that the first refrigerant absorbs or emits heat, so as to form a first refrigerant cycle; and a second refrigerant circulation part that circulates the second refrigerant, including a second compressor, a second refrigerant-water heat exchanger using the second refrigerant to perform at least one of the hot water supply operation and a heating/cooling operation, a second expander, and the cascade heat exchanger, so as to form a second refrigerant cycle, characterized in that the hot water supply device further comprises: a hot water supply part configured to perform the hot water supply operation using at least one of the first refrigerant or the second refrigerant; a water supply part that supplies water to the first refrigerant-water heat exchanger and the hot water supply part, the water supply part comprising: a water supply passage configured to receive water from a water supply source; a circulation passage in which water to be heat-exchanged with the refrigerant in the first refrigerant-water heat exchanger circulates, the circulation passage being connected to the first refrigerant-water heat exchanger; a circulation side supply passage connected to the water supply passage and extending to the circulation passage so configured to supply the water in the water supply passage to the circulation passage; and a circulation side discharge passage connected to the circulation passage configured to discharge water from the circulation passage, a hot water supply side supply passage connected to the water supply passage configured to guide water from the water supply passage to the hot water supply part; wherein water flowing in the circulation passage and water stored in the hot water supply part are supplied from the same water supply source, and wherein the refrigerants flowing through the first refrigerant-water heat exchanger and the second refrigerant-water heat exchanger are heat-exchanged with water to continuously perform the hot water supply operation without a defrosting operation. a cascade heat pump, including a first refrigerant circulation part that circulates a first refrigerant including a first compressor, a cascade heat exchanger in which heat is exchanged between the first refrigerant and a second refrigerant, a first expander, a first refrigerant-water heat exchanger configured such that the first refrigerant absorbs or emits heat, so as to form a first refrigerant cycle; and a second refrigerant circulation part that circulates the second refrigerant, including a second compressor, a second refrigerant-water heat exchanger using the second refrigerant to perform at least one of the hot water supply operation and a heating/cooling operation, a second expander, and the cascade heat exchanger, so as to form a second refrigerant cycle, a hot water supply part configured to perform the hot water supply operation using at least one of the first refrigerant or the second refrigerant; a water supply part that supplies water to the first refrigerant-water heat exchanger and the hot water supply part, the water supply part comprising: a water supply passage configured to receive water from a water supply source; a circulation passage in which water to be heat-exchanged with the refrigerant in the first refrigerant-water heat exchanger circulates, the circulation passage being connected to the first refrigerant-water heat exchanger; a circulation side supply passage connected to the water supply passage and extending to the circulation passage so configured to supply the water in the water supply passage to the circulation passage; and a circulation side discharge passage connected to the circulation passage configured to discharge water from the circulation passage, a hot water supply side supply passage connected to the water supply passage configured to guide water from the water supply passage to the hot water supply part; wherein water flowing in the circulation passage and water stored in the hot water supply part are supplied from the same water supply source, and wherein the refrigerants flowing through the first refrigerant-water heat exchanger and the second refrigerant-water heat exchanger are heat-exchanged with water to continuously perform the hot water supply operation without a defrosting operation.