A fuel cell of a fuel cell stack includes separators. Each of the separators includes a fuel gas supply section, a bridge, and a sandwiching section. A fuel gas supply passage extends through the center of the fuel gas supply section, and a fuel gas supply channel is formed in the bridge. A plurality of the fuel cells are stacked together to form a stack body. Side insulating members are provided in parallel with an extension line extending from the bridge, and along both of outer portions of the sandwiching section. The side insulating members suppress heat radiation from the fuel cells, and are used as a reference level for positioning the fuel cells at the time of stacking the fuel cells.