A nickel hydrogen secondary battery includes an electrode group including a positive electrode and a negative electrode that face each other via a separator, an outer package can that has an opening at an upper end thereof, and accommodates the electrode group therein together with an electrolyte, a sealing body including a cover plate fitted in the opening of the outer package can, and a positive electrode cap which is electrically connected to an outer surface of the cover plate, a positive electrode lead, one end portion of which is electrically connected to an inner surface of the cover plate and the other end portion of which is electrically connected to the positive electrode, and an oxygen block layer that covers at least a range where the one end portion of the positive electrode lead and the inner surface of the cover plate overlap each other, and suppresses permeation of oxygen therethrough, and a thickness of a thinnest portion of the oxygen block layer is 3 μm or more.