A unit cell of a fuel cell is formed by sandwiching a membrane electrode assembly between a first metal separator and a second metal separator. The membrane electrode assembly includes a solid polymer electrolyte membrane having a reinforcement member on both surfaces of the outer end of the solid polymer electrolyte membrane. Frame members are provided on the reinforcement member outside an anode, and a fuel gas inlet channel and a fuel gas outlet channel are formed by the frame members, at positions corresponding to a fuel gas inlet buffer and a fuel gas outlet buffer.