A fuel cell stack is constituted by stacking fuel cells including a membrane electrode assembly constituted by sandwiching an electrolyte membrane with a pair of electrodes and a pair of separators that have flow passages through which gas to be supplied to the membrane electrode assembly flows, the pair of separators being arranged across the membrane electrode assembly. The fuel cell stack includes a welded portion where the separators adjacent to one another in a stacking direction of the fuel cell are welded. The separator in the stacking direction at the welded portion has a height lower than a height of the separator other than the welded portion.