An energy storage system comprises: an alternating-current/direct-current converter; a battery; a booster; a direct-current/alternating-current converter; a power control unit; an inductor having one terminal connected to a supply terminal to which normal alternating-current power is supplied; a switching unit having one terminal connected to the other terminal of the inductor and having the other terminal connected to an input/output terminal; a current determination unit which compares an inductor current flowing through the inductor with a power recovery limit current determined by a user; and a switching control unit.