NOVELTY - A gaseous diffusion layer (13) has water-repellent carbon layer (15) containing electroconductive carbon and water-repellent material, and gaseous diffusion layer base material (14) containing water-repellent material. The layer (15) is arranged between catalyst layer (12) and base material (14). The carbon layer has center portion, at which catalyst layer is arranged, and outer edge portion located outside periphery of catalyst layer. The thickness of outer edge portion is more than thickness of center portion by 10-100 microns.    USE - For gas diffusion electrode of membrane electrode joint component (both claimed) used for polyelectrolyte fuel cell used as domestic power supply and power supply for motor vehicles.    ADVANTAGE - The gaseous diffusion layer provides fuel cell having excellent durability, stability and electric power generation capability. The decomposition deterioration of polymeric electrolyte film is suppressed.    DETAILED DESCRIPTION - A gaseous diffusion layer (13) has a water-repellent carbon layer (15) containing electroconductive carbon and water-repellent material, and a gaseous diffusion layer base material (14) containing water-repellent material. The layer (15) is arranged between catalyst layer (12) containing electrode catalyst, and base material (14). The layer (13) is used as support of catalyst layer. The carbon layer has center portion, at which catalyst layer is arranged, and outer edge portion located outside periphery of catalyst layer. The outer edge portion is formed such that portion(s) of side of catalyst layer is covered. The thickness of outer edge portion is more than thickness of center portion by 10-100 microns.    INDEPENDENT CLAIMS are included for the following:    (1) gas diffusion electrode; and    (2) membrane electrode joint component (10).    DESCRIPTION OF DRAWING(S) - The figure shows the schematic sectional view of membrane electrode joint component.    Membrane electrode joint component (10)    Polymeric electrolyte film (11)    Catalyst layer (12)    Gaseous diffusion layer (13)    Gaseous diffusion layer base material (14)    Water-repellent carbon layer (15)