A polymer electrolyte fuel cell in which neither cross leakage nor outward leakage occurs with the application of low clamping pressures. The polymer electrolyte fuel cell a membrane electrode assembly (MEA) including a polymer electrolyte membrane, a gasket covering the periphery of the electrolyte membrane, and an anode and cathode attached to the electrolyte membrane; and conductive separator plates sandwiching the MEA therebetween. The gasket has seal ribs surrounding each of the manifold apertures, the anode and the cathode, as well as seal ribs formed on both sides of each of gas passages connecting the fuel gas manifold apertures with the anode and gas passages connecting the oxidant gas manifold apertures with the cathode. These seal ribs, except for in the gas passages, are pressed against the separator plates by clamping pressure of the cell stack to form gas sealing sections.