A storage water heater comprising: a hot water storage tank that stores hot water; heating means for heating hot water stored in the hot water storage tank; a hot water supply heat exchanger for performing heat exchange between hot water supplied from an upper portion of the hot water storage tank and supply water; a supply water conduit that guides the supply water to a hot water supply terminal via the hot water supply heat exchanger; a hot water supply heat source conduit that guides water from the upper portion of the hot water storage tank to a lower portion of the hot water storage tank via the hot water supply heat exchanger; a hot water supply heat source pump that circulates water in the hot water supply heat source conduit; and pump control means for, in a hot water supply operation of supplying hot water to the hot water supply terminal, calculating an output of the hot water supply heat source pump, the output bringing a heat source-side flow rate that is a flow rate of hot water flowing in the hot water supply heat source conduit to a target flow rate, for each control interval and controlling the hot water supply heat source pump based on the calculated output, wherein the pump control means includes control interval changing means for changing the control interval based on an amount of temporal change in a hot water supply-side flow rate that is a flow rate of supply water flowing in the supply water conduit, characterized in that if the amount of temporal change in the hot water supply-side flow rate exceeds a threshold value, the control interval changing means changes the control interval from a first control interval to a second control interval that is shorter than the first control interval. a hot water storage tank that stores hot water; heating means for heating hot water stored in the hot water storage tank; a hot water supply heat exchanger for performing heat exchange between hot water supplied from an upper portion of the hot water storage tank and supply water; a supply water conduit that guides the supply water to a hot water supply terminal via the hot water supply heat exchanger; a hot water supply heat source conduit that guides water from the upper portion of the hot water storage tank to a lower portion of the hot water storage tank via the hot water supply heat exchanger; a hot water supply heat source pump that circulates water in the hot water supply heat source conduit; and pump control means for, in a hot water supply operation of supplying hot water to the hot water supply terminal, calculating an output of the hot water supply heat source pump, the output bringing a heat source-side flow rate that is a flow rate of hot water flowing in the hot water supply heat source conduit to a target flow rate, for each control interval and controlling the hot water supply heat source pump based on the calculated output, wherein the pump control means includes control interval changing means for changing the control interval based on an amount of temporal change in a hot water supply-side flow rate that is a flow rate of supply water flowing in the supply water conduit, characterized in that if the amount of temporal change in the hot water supply-side flow rate exceeds a threshold value, the control interval changing means changes the control interval from a first control interval to a second control interval that is shorter than the first control interval.