The invention provides a secondary battery including a more reliable current interrupt mechanism. A positive electrode sheet is electrically connected to a positive terminal (7) via a positive electrode current collector (6), a deformable plate (21), and a conductive member (20). When the pressure inside a battery is higher than a predetermined value, the deformable plate (21) is deformed toward a sealing plate (3) and an annular groove (6x) formed on a base portion (6a) of the positive electrode current collector (6) is broken due to deformation so that a conductive path between the positive electrode sheet and the positive terminal (7) is disconnected. A first insulating member (22) disposed between the deformable plate (21) and the base portion (6a) of the positive electrode current collector (6) includes a first rotation preventing protrusion (30a) on a surface thereof on a wound electrode body (1)side and outside an outer circumferential edge of the base portion (6a) of the positive electrode current collector (6).