An energy storage device includes a positive electrode current collector and a negative electrode current collector which respectively have electric conductivity and are joined to each other, and cover members. The energy storage device includes swaged joint portions which join the positive electrode current collector and the cover members to each other, and are engaged with each other by fitting engagement by a concavo-convex fitting engagement structure which projects from the positive electrode current collector toward the cover members, and swaged joint portions which join the negative electrode current collector and the cover members to each other and, are engaged with each other by fitting engagement by a concavo-convex fitting engagement structure which projects from the negative electrode current collector toward the cover members. The cover members respectively include a strip-shaped projection which forms a rigidity changing part on the side of the swaged joint portion.