A fuel cell stack (10) is comprised of a plurality of power generating units (12) which are stacked along the horizontal direction. A corrugated passage groove (44a) having a shape corresponding to the shape of the underside surface of a corrugated passage groove (36a) of a first fuel gas passage (36) is formed in a surface (14b) of a first metal separator (14). A corrugated passage groove (44b) having a shape corresponding to the shape of the underside surface of a corrugated passage groove (66a) of a second oxidant gas passage (66) is formed in a surface (20b) of a third metal separator (20). The corrugated passage grooves (44a, 44b) overlap one another to define a refrigerant passage (44). An oxidant gas inlet port (30a) and a fuel gas inlet port (32a) are provided in the upper portion of the power generating unit (12), and an oxidant gas outlet port (30b) and a fuel gas outlet port (32b) are provided in the lower portion of the power generating unit (12). A refrigerant inlet port (34a) and a refrigerant outlet port (34b) are formed in each of the left and right portions of power generating unit (12).