A hot water supply system, comprising: - a heat pump apparatus having a first refrigerant circuit in which a compressor, a first radiator, an expansion mechanism, and an evaporator are sequentially connected by pipes and through which circulates a first refrigerant heated by the compressor; - a second refrigerant circuit in which the first radiator is connected with a second radiator that heat-exchanges with hot water storage tank water stored in a hot water storage tank, and in which circulation of a second refrigerant heated by the first refrigerant passing through the first radiator causes the hot water storage tank water to be heated by the second radiator; and - a tank water temperature detection sensor that detects a tank water temperature of the hot water storage tank water, and a control apparatus, characterized in that the hot water supply system comprises: - an operation control unit that, when the tank water temperature of the hot water storage tank water detected by the tank water temperature detection sensor is equal to or lower than a first temperature, operates the hot water supply system with a first operating method until the tank water temperature rises to a second temperature which is higher than the first temperature, the first operating method operating the heat pump apparatus with lower output than a rated operation and with a load rate having a higher coefficient of performance than the rated operation by operating the compressor at a lower frequency than the rated frequency, and when the tank water temperature exceeds the second temperature, operates the hot water supply system with a second operating method until the tank water temperature rises to a third temperature which is higher than the second temperature, the second operating method operating the heat pump apparatus with higher heating capability than the first operating method, by operating the compressor at the rated or upper limit frequency or at a frequency higher than that for the first operating method. - a heat pump apparatus having a first refrigerant circuit in which a compressor, a first radiator, an expansion mechanism, and an evaporator are sequentially connected by pipes and through which circulates a first refrigerant heated by the compressor; - a second refrigerant circuit in which the first radiator is connected with a second radiator that heat-exchanges with hot water storage tank water stored in a hot water storage tank, and in which circulation of a second refrigerant heated by the first refrigerant passing through the first radiator causes the hot water storage tank water to be heated by the second radiator; and - a tank water temperature detection sensor that detects a tank water temperature of the hot water storage tank water, and - an operation control unit that, when the tank water temperature of the hot water storage tank water detected by the tank water temperature detection sensor is equal to or lower than a first temperature, operates the hot water supply system with a first operating method until the tank water temperature rises to a second temperature which is higher than the first temperature, the first operating method operating the heat pump apparatus with lower output than a rated operation and with a load rate having a higher coefficient of performance than the rated operation by operating the compressor at a lower frequency than the rated frequency, and when the tank water temperature exceeds the second temperature, operates the hot water supply system with a second operating method until the tank water temperature rises to a third temperature which is higher than the second temperature, the second operating method operating the heat pump apparatus with higher heating capability than the first operating method, by operating the compressor at the rated or upper limit frequency or at a frequency higher than that for the first operating method.