SECONDARY BATTERY

A secondary battery includes a flat wound electrode body in which an electrode sheet is wound, and an electrode terminal. The electrode sheet has a current collector, an electrode active material layer which is formed on a surface of the current collector, and a non-formation portion in which the electrode active material layer is not formed on the surface of the current collector. The wound electrode body has a first end portion in which a rounded portion is formed. A first slit is formed along a winding direction in the non-formation portion at the first end portion. A flat surface portion to which the electrode terminal is joined is provided in a portion positioned further toward opposite than the first slit from the electrode active material layer in a portion of the non-formation portion at the first end portion.