An energy storage device includes an electrode assembly that includes a sheet-like first electrode and a sheet-like second electrode, the first electrode and the second electrode being alternately layered. Each of the first electrode and the second electrode includes a sheet-like current collecting substrate, and the current collecting substrate of the first electrode is bent toward one side in a layered direction in at least a part of an end portion of the first electrode. The electrode assembly also includes an extension portion formed in such a manner that the current collecting substrate of the second electrode extends outward more than the end portion of the first electrode.