An energy storage device for uniformly controlling internal temperature of a container by controlling a flow of a cooling air current includes: racks for accommodating a plurality of battery packs; a container for accommodating the racks; an access floor provided at a lower part of the container for supplying a cooling air current to the racks through supply openings; and a distribution plate provided under the access floor to distribute an amount of the cooling air current that is supplied from under the access floor.