Provided is a fuel cell stack having reduced thickness and weight and an improved output density. The fuel cell stack according to the present invention includes two or more stacked fuel cell layers, and is characterized in that at least one of the fuel cell layers is formed by arranging two or more composite unit cells in an identical plane with a gap provided therebetween, that the composite unit cell includes a plurality of unit cells and a fuel supply portion for supplying fuel to anode electrodes of the unit cells, and that the anode electrodes of the plurality of unit cells are arranged to face the fuel supply portion.