A secondary battery of a proton conductive polymer, wherein a positive electrode 2 and a negative electrode 4 are arranged facing to each other via a separator in an electrolytic solution and only a proton in a π conjugated polymer or a proton of a hydroxyl group in a hydroxyl-containing macromolecular as an active material of an electrode in the positive and negative electrodes participates in a charge/discharge; the secondary battery uses a membrane, which has acid resistance, oxidation resistance and a functional group having cation exchange function, as the separator 3.