A cell stack in which a plurality of cells may have a cylindrical shape and may include gas flow passages may be arranged uprightly and may be electrically connected may include: a manifold configured to fix lower ends of the plurality of cells and supply gas to the gas flow passages of the plurality of cells, and a gas supply pipe configured to supply the gas to the manifold. The gas supply pipe may include one end connected to a gas supply portion and another end inserted into a first through hole provided in the manifold, and may be joined to the manifold via a first joining portion. The gas supply pipe may include a first protruding portion protruding toward an inner side of the gas supply pipe and located at a position corresponding to the first joining portion in any cross-section along an insertion direction of the gas supply pipe.