A fuel cell stack constituted by fastening a laminated cell, is disclosed. The electrode of the cell has a catalyst electrode layer and a porous gas diffusion layer and supporting a polymer electrolyte membrane (1) from both sides. A separator (3) of the cell has a gas passage (6, 7) which supplies fuel gas or oxidizer gas to the gas diffusion layer. The gas diffusion layer (2b) is constituted such that when a load is applied and removed in the lamination direction of the cell, an amount of change in a thickness of the gas diffusion layer in a non-loaded state before and after the load is applied falls to or below a predetermined value. The gas diffusion layer (2b) is manufactured by repeating a cycle of applying and removing a load on the gas diffusion layer in the lamination direction of the cell before laminating the cell. The cycle is repeated until an amount of change in a thickness of the gas diffusion layer in a non-loaded state before and after the load is applied falls to or below a predetermined value. The gas diffusion layer (2b) is prevented from swelling into the gas passage.