Provided is an energy storage device which can sufficiently reduce a resistance of a current path. An energy storage device includes: an outer case having a lid plate on which an external terminal is mounted; a plate having a tab and housed in the outer case; a conductive shaft portion penetrating the lid plate and having one end thereof connected to the external terminal; and a conductive plate portion housed in the outer case, and having a first surface to which the other end of the conductive shaft portion is connected and a second surface to which the tab is connected, wherein a size of the conductive plate portion and a size of the tab are respectively set larger than a size of the external terminal in a planar direction of the lid plate.