A charge/discharge control method for a charge/discharge element includes receiving a request value (Pfr) of a frequency adjustment capacity according to a system frequency (f) of an electric power system () based on a priority degree (β) and the request value (Pfr) being received, the priority degree indicating a degree at which charging or discharging of an own element (EV) is prioritized over charging or discharging of another charge/discharge element (EV, EV, . . . ), correcting the output property to increase an upper limit value or a lower limit value of an output range as the priority degree (β) is higher, and performing charging or discharging with an output determined based on a deviation (Δf) between the system frequency (f) measured at a connection end to the electric power system () and a reference frequency (fref) of the electric power system () and the output property after the correction.
