A hermetically sealed battery with an opening-sealing unit 10 according to the present invention comprises a PTC element ring 16 elastically clamped between the flange 12a of a positive electrode cap 12 and a fold portion 11d formed at the peripheral portion 11c of a bottom plate 11, such that when the temperature of the PTC element rises due to overcurrent or overheating, the PTC element ring 16 can easily expand, thereby tripping the large current with its resistance capacity increased to a predetermined level at a predetermined temperature, thereby enhancing operational security of the battery.