A fuel cell stack capable of giving improved impact resistance and vibration resistance without causing the space occupied by the fuel cell stack to be increased. In a fuel cell stack for mounting in a vehicle in which a plurality of fuel cell units, each of which is formed by interposing a solid polymer electrolyte membrane between an anode electrode and a cathode electrode, are stacked in a horizontal direction with separators placed between each, mounting members used for installation are provided at backup plates that are outside fastening structure portions that are provided at both ends along the direction in which the fuel cell units are stacked, and an intermediate supporting member used for installation is additionally provided at an intermediate portion along the direction in which the fuel cell units are stacked.