The present invention provides a battery, in which swelling or expansion of side surface of a battery case when the battery is charged is reduced. The invention provides a sealed battery, accommodating a battery element of flat shape, said battery element comprising a positive electrode and a negative electrode being laminated on each other with a separator interposed between them and being wound together, characterized in that a recessed portion is formed on a side surface of a battery case running in parallel to a flat surface of the battery element, said recessed portion having a central axis running in parallel to said flat surface and being positioned on a surface passing through the center of the battery case and running perpendicularly to the surface in parallel to the flat surface of the battery element.
