A method for equalizing capacities of electric storage devices that are connected in series in an electric storage device assembly charged and discharged by a charger/discharger includes charging/discharging the electric storage device assembly at a charging/discharging rate of 1 C or lower, individually measuring voltages of the electric storage devices, respectively, determining whether a time rate of change in voltage of one electric storage device of the electric storage devices has reached a time-rate-of-change reference value and then a time rate of change in voltage of another electric storage device of the electric storage devices has reached the time-rate-of-change reference value, and individually discharging, based on a determining result, the electric storage device by a discharging circuit provided separately from the discharger.