The opening of a cylindrical battery case 1 with a bottom is sealed by a seal assembly 5. The seal assembly 5 has an upper valve plate 13, a lower valve plate 15, and a bottom plate 16. The bottom plate 16 has inner gas vent holes 21. When the inner gas vent holes 21 are viewed from the axial direction of the battery case 1, at least a part of each inner gas vent hole 21 overlaps a valve-hole forming portion 15b of the lower valve plate 15. With this configuration, for example, even when an electrode assembly 20 is pushed up by increased internal pressure of the battery to push up the bottom plate 16, the valve hole is not closed.