NOVELTY - The method comprises: bonding a reinforcement (131) having an opening in its central part to a proton exchange membrane and an electrode placed against a face of the membrane so that an inner edge of the reinforcement covers a periphery of the electrode with an overflow on the proton exchange membrane; forming a recess in a periphery of a gas diffusion layer (21) by a method of forming a wet watermark in the gas diffusion layer; and placing the gas diffusion layer so that the recess is formed directly below the inner edge of the reinforcement.    USE - The method is useful for manufacturing a fuel cell (claimed) that is useful in automotive or aerospace applications.    ADVANTAGE - The method is capable of economically manufacturing the fuel cell with reduced size and weight, improved performance and prolonged service life.    DETAILED DESCRIPTION - The method comprises: bonding a reinforcement (131) having an opening in its central part to a proton exchange membrane and an electrode placed against a face of the membrane so that an inner edge of the reinforcement covers a periphery of the electrode with an overflow on the proton exchange membrane; forming a recess in a periphery of a gas diffusion layer (21) by a method of forming a wet watermark in the gas diffusion layer; and placing the gas diffusion layer so that the recess is formed directly below the inner edge of the reinforcement. The step of forming the watermark comprises applying a layer of an aqueous solution including carbon fibers and a binder material and solidifying components of the aqueous solution for forming the gas diffusion layer. The gas diffusion layer includes a recess formed to a depth of 25-75 mu m and with a width of 500-3000 mu m, and has a homogeneous disposed composition. The gas diffusion layer comprises a first face in which the recess is formed, and a second face. A portion of the second face to levelness of the recess is in alignment with a middle portion of the second face.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic sectional view of a fuel cell.    Gas diffusion layers (21, 22)    Guide plates (101 102)    Cathode (111)    Anode Guide plates (112)    Reinforcements. (131, 132)