The invention provides an energy storage element which allows a relatively large tolerance, is easy to manufacture and can be manufactured with low cost. A non-aqueous electrolyte secondary battery (1) includes: a container (30); an electrode assembly (11); an electrode terminal (23); a current collector (12); and an internal insulation sealing member (13) insulating the container and the current collector. The container includes a wall having an outer surface with a protrusion part (21) protruding outward from the outer surface and an inner surface with a recess part (21x) formed correspondingly in position to the protrusion part. The recess part has an outermost bottom surface (21y) and an inner side surface formed continuously between the bottom surface and the inner surface of the wall of the container. At least part of the inner side surface of the recess part is tilted to the protrusion direction of the protrusion part.; The internal insulation sealing member is between the current collector and the recess part of the container, and has side wall parts parallel to the at least part of the inner side surface.