A fuel cell stack is provided having a plurality of unit cells stacked in a horizontal direction. Each unit cell includes an electrolyte membrane having two surfaces and a peripheral edge, electrodes provided on both surfaces of the electrolyte membrane, frame-shaped members provided on both surfaces of the electrolyte membrane adjacent to the respective electrodes and adjacent the peripheral edge of the electrolyte membrane, separators provided on the electrodes and the frame-shaped members and having a reactant gas passage for supplying a reactant gas to each of the electrodes, and a manifold formed in the stacking direction in fluid communication with the reactant gas passage. The manifold includes a horizontal edge portion in fluid communication with the reactant gas passage.