A conductive member (61) is disposed near a side of the sealing plate (2) facing an electrode assembly with a first insulating member (10) disposed therebetween. The conductive member (61) has a conductive-member opening portion (61f) at a side thereof facing the electrode assembly. The conductive-member opening portion (61f) of the conductive member (61) is sealed by a deformation plate (62). The deformation plate (62) is connected to a first positive-electrode current collector (6a), which is electrically connected to positive electrode plates. The deformation plate (62) includes an annular rib (62b) that projects toward the electrode assembly at the outer peripheral edge thereof. The deformation plate (62) also includes an annular thin portion (62c) in a region inside the annular rib (62b).