A fuel cell comprises a single cell including a membrane assembly electrode unit comprising a fuel electrode to which an aqueous methanol solution is supplied as a fuel, an air electrode to which an oxidizing gas is supplied, and an electrolyte membrane interposed between the electrodes, a fuel separator and an oxidizing gas separator disposed at both sides of the membrane assembly electrode unit, and seal members respectively disposed between the membrane assembly electrode unit and the fuel separator and between the membrane assembly electrode unit and the oxidizing gas separator. The seal member includes a specific copolymer of a monomer containing a metal element.