A nonaqueous electrolyte secondary battery includes a conductive outer can (12), an electrode body (40) in the outer can (12), a conductive seal plate (14) tightly closing an open end of the outer can (12), and a cathode external terminal (20) on the seal plate (14). The battery further includes a current cutoff mechanism (CID). The CID is located on the electrical conduction pathway between the cathode external terminal (20) and the electrode body (40) and interrupts the electrical coupling therebetween in response to an increased internal pressure in the battery. The CID includes a thin portion (14a) of the seal plate (14) and a diaphragm (50). The diaphragm deforms to interrupt the electrical coupling between the cathode external terminal (20) and the electrode body (40) in response to the increase in the internal pressure in the battery. A cathode collector lead (28) electrically couples the electrode body (40) and the seal plate (14), and the seal plate (14) connects the diaphragm (50) and the cathode collector lead (28).