A fuel cell stack includes a stack body of power generation cells stacked in a horizontal direction. An oxygen-containing gas flow field is formed in the fuel cell stack, for allowing an oxygen-containing gas to flow along an electrode surface of a membrane electrode assembly. A plurality of oxygen-containing gas discharge passages for discharging the oxygen-containing gas as a reactant gas pass through the fuel cell stack in a stacking direction of the power generation cells. Each of the oxygen-containing gas discharge passages is connected to an outlet. The plurality of oxygen-containing gas discharge passages are connected together by a first connection channel at an end opposite to the outlet.