An energy storage device includes: an electrode assembly which includes: an approximately rectangular positive electrode; an approximately rectangular negative electrode which is stacked alternately with the positive electrode; and a strip-like elongated separator having a base material layer and an inorganic layer which is made to overlap with the first base material layer, wherein the elongated separator is arranged between the positive electrode and the negative electrode, and the base material layer of the elongated separator faces the negative electrode in an opposed manner between the positive electrode and the negative electrode.