receiving a request value of a frequency adjustment capacity according to a system frequency of an electric power system, the request value being broadcast-transmitted to a plurality of charge/discharge elements connected to an electric wire of the electric power system;

determining an output property of charging/discharging with respect to the system frequency, based on a priority degree and the request value being received, the priority degree indicating a degree at which charging or discharging of an own element is prioritized over charging or discharging of another charge/discharge element;

correcting the output property to increase an upper limit value or a lower limit value of an output range as the priority degree is higher; and

performing charging or discharging with an output determined based on a deviation between the system frequency measured at a connection end to the electric power system and a reference frequency of the electric power system and the output property after the correction.