A power estimating apparatus includes a functional unit, at least one converter, a detection unit, and an estimating unit. The functional unit uses an alternating-current power supply. The at least one converter is connected to a branch point between the alternating-current power supply and the functional unit and includes a smoothing capacitor so as to convert an alternating current from the alternating-current power supply into a direct current. The detection unit obtains a total amount of currents supplied to the functional unit and the at least one converter. The estimating unit uses the total amount to estimate an amount of the current supplied to the functional unit. The total amount is obtained by the detection unit in a charge and discharge period during which the smoothing capacitor performs a charge and discharge operation.