A fuel cell includes: a membrane electrolyte assembly which includes a polymer electrolyte membrane and a pair of catalyst electrodes between which the polymer electrolyte membrane is held and separators between which the membrane electrolyte assembly is held. The first separator includes first gas flow channels and second gas flow channels which are adjacent to the first gas flow channels, the first and second gas flow channels supplying an oxidizing gas or a fuel gas to the membrane electrolyte assembly. The first and second gas flow channels are parallel to each other and are alternately arranged, the first gas flow channels are larger in cross sectional area than the second gas flow channels. The second separator includes first gas flow channels parallel to the first and second gas flow channels of the first separator, and second gas flow channels which are adjacent to the first gas flow channels, the first and second gas flow channels supplying an oxidizing gas or a fuel to the membrane electrolyte assembly. The first and second gas flow channels are parallel to each other and are alternately arranged and the oxidizing gas or fuel gas supplied in the first and second gas flow channels of the first separator flows in an opposite direction to the oxidizing gas or fuel gas supplied in the first and second gas flow channels of the second separator.