To provide a hot water storage type water heater capable of simultaneously performing a heating-up operation of a hot water storage tank, a reheating operation of a bathtub, and a heating operation by a heating unit by one tank circulation pump.

This hot water storage type water heater comprises a heating-up circuit including a first three-way valve connected with a lower portion of the hot water storage tank at its first inflow port, the tank circulation pump connected with an outflow port of the first three-way valve at its suction port, a second three-way valve connected with a discharge port of the tank circulation pump at its inflow port, and a heat exchanger for heating-up connected with the first outflow port of the second three-way valve at its inflow port and connected with an upper portion of the hot water storage tank at its outflow port, a heat source circuit including a first three-way valve connected with an upper portion of the hot water storage tank at its second inflow port, a tank circulation pump connected with an outflow port of the first three-way valve at its suction port, and a second three-way valve connected with a discharge port of the tank circulation pump at its inflow port and connected with a lower portion of the hot water storage tank at its second outflow port, and an utilization-side heat exchanger connected in the heat source circuit in series.