To provide a proton conductor capable of exerting excellent ion conductivity even without humidification or at relative humidity below 50% at an operation temperature of 100-300°C; and to provide a fuel cell using the proton conductor.

This proton conductor comprises a condensed phosphoric acid, phosphoric acid ions, metal ions, and proton coordinating molecules. For the proton coordinating molecules, imidazole, an imidazole derivative, an imidazolium salt, an imidazolium derivative, pyridine, a pyrydine derivative, a pyridinium salt, a pyridinium derivative salt, tertiary alkyl ammonia, or a quaternary ammonium salt are available.

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