A method of managing electric power for managing power, within a group, said power is to be used by a first user with a power storage system and a second user without the power storage system, the method including: (a) collecting data regarding load power of the first user and the second user and calculating total load power within the group; (b) determining whether the total load power is equal to or greater than a peak cut power; (c) determining whether a value of [total load power−peak cut power] is smaller than the load power of the first user when determination in the step (b) is Yes; and (d) causing the power storage system to discharge at the value of [total load power−peak cut power], when determination in the step (c) is Yes.