A nickel-zinc battery comprising: a positive electrode comprising nickel hydroxide and/or nickel oxyhydroxide; a positive-electrode electrolytic solution comprising an alkali metal hydroxide, the positive electrode being immersed in the electrolytic solution; a negative electrode comprising zinc and/or zinc oxide; a negative-electrode electrolytic solution comprising an alkali metal hydroxide, the negative electrode being immersed in the electrolytic solution; a hermetic container accommodating the positive electrode, the positive-electrode electrolytic solution, the negative electrode, and the negative-electrode electrolytic solution; a separator exhibiting hydroxide ion conductivity and water impermeability, the separator being disposed in the hermetic container so as to separate a positive-electrode chamber (24; 24a-c) accommodating the positive electrode and the positive-electrode electrolytic solution from a negative-electrode chamber (26; 26a-b) accommodating the negative electrode and the negative-electrode electrolytic solution; and a porous substrate disposed on a surface of the separator facing toward the positive electrode, characterized in that the positive-electrode chamber (24; 24a-c) has an extra positive-electrode space having a volume that meets a variation in amount of water in association with reaction at the positive electrode during charge and discharge of the battery, and the negative-electrode chamber (26; 26a-b) has an extra negative-electrode space having a volume that meets a variation in amount of water in association with reaction at the negative electrode during charge and discharge of the battery and the extra positive-electrode space has a volume greater than the amount of water that will decrease in association with reaction at the positive electrode during the discharge of the battery; the extra positive-electrode space is preliminarily filled with an amount of the positive-electrode electrolytic solution that will decrease during the discharge of the battery; the extra negative-electrode space has a volume greater than the amount of water that will increase in association with reaction at the negative electrode during the discharge of the battery; and the extra negative-electrode space is not preliminarily filled with the negative-electrode electrolytic solution. a positive electrode comprising nickel hydroxide and/or nickel oxyhydroxide; a positive-electrode electrolytic solution comprising an alkali metal hydroxide, the positive electrode being immersed in the electrolytic solution; a negative electrode comprising zinc and/or zinc oxide; a negative-electrode electrolytic solution comprising an alkali metal hydroxide, the negative electrode being immersed in the electrolytic solution; a hermetic container accommodating the positive electrode, the positive-electrode electrolytic solution, the negative electrode, and the negative-electrode electrolytic solution; a separator exhibiting hydroxide ion conductivity and water impermeability, the separator being disposed in the hermetic container so as to separate a positive-electrode chamber (24; 24a-c) accommodating the positive electrode and the positive-electrode electrolytic solution from a negative-electrode chamber (26; 26a-b) accommodating the negative electrode and the negative-electrode electrolytic solution; and a porous substrate disposed on a surface of the separator facing toward the positive electrode, characterized in that the positive-electrode chamber (24; 24a-c) has an extra positive-electrode space having a volume that meets a variation in amount of water in association with reaction at the positive electrode during charge and discharge of the battery, and the negative-electrode chamber (26; 26a-b) has an extra negative-electrode space having a volume that meets a variation in amount of water in association with reaction at the negative electrode during charge and discharge of the battery and the extra positive-electrode space has a volume greater than the amount of water that will decrease in association with reaction at the positive electrode during the discharge of the battery; the extra positive-electrode space is preliminarily filled with an amount of the positive-electrode electrolytic solution that will decrease during the discharge of the battery; the extra negative-electrode space has a volume greater than the amount of water that will increase in association with reaction at the negative electrode during the discharge of the battery; and the extra negative-electrode space is not preliminarily filled with the negative-electrode electrolytic solution.