A heat pump water heater performing heating so as to make hot water in a hot water storage tank, having a preset stored hot water temperature target value and a preset stored hot water amount target value, by using as much electric power in a time period in which an electric power rate is relatively as inexpensive as possible, characterized in that it comprises: acquisition means configured to acquire a minimum heat storage amount per day from past use result data including a heat storage amount or a remaining hot water amount and a hot water supply load; target value change means configured to change at least one of the stored hot water temperature target value and the stored hot water amount target value when the minimum heat storage amount is higher than a predetermined range; and calculation means configured to perform calculation of a minimum heat storage amount of a day by using the stored hot water temperature target value and the stored hot water amount target value after change and a hot water supply load of a day in the past use result data, wherein, if the minimum heat storage amount is higher than an upper limit value of the predetermined range, the target value change means decreases the stored hot water temperature target value with priority until the minimum heat storage amount obtained by calculation by the calculation means falls within the predetermined range, and if the stored hot water temperature target value reaches a predetermined lower limit value, the target value change means decreases the stored hot water amount target value, and if the minimum heat storage amount is lower than a lower limit value of the predetermined range, the target value change means increases the stored hot water amount target value with priority until the minimum heat storage amount obtained by calculation by the calculation means falls within the predetermined range, and if the stored hot water amount target value reaches a predetermined upper limit value, the target value change means increases the stored hot water temperature target value. acquisition means configured to acquire a minimum heat storage amount per day from past use result data including a heat storage amount or a remaining hot water amount and a hot water supply load; target value change means configured to change at least one of the stored hot water temperature target value and the stored hot water amount target value when the minimum heat storage amount is higher than a predetermined range; and calculation means configured to perform calculation of a minimum heat storage amount of a day by using the stored hot water temperature target value and the stored hot water amount target value after change and a hot water supply load of a day in the past use result data, wherein, if the minimum heat storage amount is higher than an upper limit value of the predetermined range, the target value change means decreases the stored hot water temperature target value with priority until the minimum heat storage amount obtained by calculation by the calculation means falls within the predetermined range, and if the stored hot water temperature target value reaches a predetermined lower limit value, the target value change means decreases the stored hot water amount target value, and if the minimum heat storage amount is lower than a lower limit value of the predetermined range, the target value change means increases the stored hot water amount target value with priority until the minimum heat storage amount obtained by calculation by the calculation means falls within the predetermined range, and if the stored hot water amount target value reaches a predetermined upper limit value, the target value change means increases the stored hot water temperature target value.