A fuel cell stack includes a plurality of single cells stacked and a manifold. The plurality of single cells each include a first separator including a seal portion surrounding the manifold and including a hollow protrusion and a fluid passage portion allowing the fluid to flow between the manifold and a space on the opposite side of the seal portion from the manifold via the hollow of the seal portion, a second separator disposed on the side opposite to the side on which the seal portion projects, of the first separator, and an electric insulating frame disposed on the opposite side of the second separator from the first separator. The second separator includes a flat-and-bulge portion in a surface facing the seal portion, along an abutment region of the seal portion and the electric insulating frame.