To provide high ion conductive solid electrolyte made of proton (hydrogen ion) or the like, especially at low cost, and showing high conductivity, a fuel cell as well as other electrochemical systems using this solid electrolyte.

The high ion-conductive solid electrolyte, as a basis, comprises at least one or more inorganic compounds selected from silicic acid compound, tungstic acid compound, or zirconic acid compound, and a complex compound containing polyvinyl alcohol, and other constituents than polyvinyl alcohol having sulfonic acid group. Concretely, the structure includes an organic compound having a sulfonic acid group other than polyvinyl alcohol, and the organic compound having the sulfonic acid group is soluble in water.

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