A fuel cell includes a laminated, plate-shaped membrane electrode assembly and first and second separator plates sandwiching the membrane electrode assembly. The membrane electrode assembly includes a polymer electrolyte membrane; first and second electrode layers sandwiching the polymer electrolyte membrane; and first and second gas-diffusion layers disposed on an outer side of the electrode layers, respectively. The first and second gas-diffusion layers are made of an air-permeable metallic material. An arithmetic average roughness Ra of a surface of the air-permeable metallic material on the side contacting one of the electrode layers is in a range of 0.1 .mu.m.ltoreq.Ra.ltoreq.1.0 .mu.m.