A fuel cell having a capability of making uniform a water distribution in an in-plane direction of a polymer electrolyte membrane and supplying a reactive gas to an air electrode catalyst layer efficiently is provided. The fuel cell of the present invention has a polymer electrolyte membrane, a pair of catalyst electrodes, and a pair of metal separators. An air electrode separator has an oxidizing gas flow channel used to supply an oxidizing gas to the catalyst electrodes. The oxidizing gas flow channel is formed in such a manner that a flow channel near an oxidizing gas supply manifold and a flow channel near an oxidizing gas exhaust manifold are adjacent to each other in the same plane, and is formed in an S-shaped or spiral pattern.