In a polymer electrolyte fuel cell, at least one of the anode side separator plate and cathode side separator plate is formed with a main surface having a convex shape protruding toward a gas diffusion layer, and a peripheral edge portion surrounding the main surface. An average thickness of the main surface is made to be thicker than an average thickness of the peripheral edge portion. And a difference .DELTA.t between the thickest part of the main surface and an average thickness of the peripheral edge portion is made to be 5-30 .mu.m.