To provide a power storage device which enables a worker to easily conduct welding work for sealing an opening and improves the productivity.

A secondary battery 10 includes a peripheral wall side inclined surface 13f which narrows a storage part S of a body member 13 in a direction from the exterior toward the interior of a case 11. Further, a lid member 14 includes a lid side inclined surface 14c which narrows the lid member 14 in a direction from the exterior toward the interior of the case 11. The lid member 14 is welded at a position that is spaced away from an opening end edge of the body member 13 so as to be located at the inner side of the case 11 than the opening end edge of the body member 13.