An object is to equalize the level of cooling along a top-bottom direction of a fuel cell stack. A fuel cell stack has an anode-side separator placed between a plurality of membrane electrode assemblies. The anode-side separator comprises a separator center area that is arranged to face a power generation area of the membrane electrode assembly; an outer peripheral portion that is extended from the separator center area to outer periphery and has a plurality of openings for cooling medium supply manifolds; and a rib that is firmed from a beam portion provided to separate the adjacent openings for cooling medium supply manifolds from each other, over an area between the openings for cooling medium supply manifolds and the separator center area.