The present invention provides an electrolyte membrane of a solid oxide fuel cell that excels in output performance. There is provided a solid oxide fuel cell comprising a single cell having an air electrode disposed on a surface of an electrolyte membrane and a fuel electrode disposed on the other surface the electrolyte membrane, and an interconnector having a role of electrical connection; wherein the electrolyte membrane is provided with a first layer composed of a material having an oxygen-ionic conductivity of S1 on the air-electrode side, a third layer composed of a material having an oxygen-ionic conductivity of S3 on the fuel-electrode side, and a second layer composed of a material containing at least zirconia and having an oxygen-ionic conductivity of S2 between the first layer and the third layer; and wherein the oxygen-ionic conductivity of S1 and the oxygen-ionic conductivity of S2 have a relationship of S1>S2, and the oxygen-ionic conductivity of S3 and the oxygen-ionic conductivity of S2 have a relationship of S3>S2.