A material which conducts protons or oxide ions with high ionic conductivity and is excellent in moisture resistance and reduction resistance is provided. A perovskite oxide represented by the formula (1): BaZr.sub.aCe.sub.bM.sup.1.sub.cL.sup.1.sub.dO.sub.3-.alpha. (1) (wherein M.sup.1 is at least one member selected from the group consisting of rare earth elements, In, Mn, Fe, Co, Ni, Al and Ga, L.sup.1 is at least one member selected from the group consisting of P, B and N and a, b, c, d and a satisfy 0.ltoreq.a<1.2, 0