The purpose of the invention is to allow a pressure sensitive current interrupting mechanism to quickly and reliably operate before a battery inner pressure rises significantly by allowing carbon dioxide to easily flow to the outside of a flat wound electrode body, said carbon dioxide being generated by the decomposition of lithium carbonate in a positive electrode mixture layer when, for example, a secondary battery is overcharged. The nonaqueous electrolyte secondary battery (10) of one embodiment of the present invention has a pressure sensitive current interrupting mechanism. A positive electrode core-body exposed portion (15) is formed at one end of a flat wound electrode body (14) and a negative electrode core-body exposed portion (16) at the other end thereof. A positive electrode mixture layer (11a) contains lithium carbonate. A protection layer (11b) is formed on the positive electrode core-body exposed portion (15) at a position facing a separator (13) along the boundary between the positive electrode core-body exposed portion (15) and the positive electrode mixture layer (11a).