The present invention provides a fuel cell comprising a pair of separators sandwiching outsides of a membrane electrode assembly composed of a pair of electrodes provided on both sides of a solid polymer electrolyte membrane, an outer seal member sandwiched by a pair of separators at a position surrounding an outer periphery of the membrane electrode assembly, an inner seal member sandwiched by one of the pair of separators and an outer periphery of the electrolyte membrane, and a backing member opposing to the inner seal member interposing the electrolyte membrane, wherein steps are formed at contact surfaces of the inner seal member and the outer seal member on one of the pair of separators.