Low production cost, has a sufficient conductivity and gas diffusivity, and an object thereof is structural change of the porous electrode substrate to provide a porous electrode substrate and its manufacturing method showing a small good power generation performance . And the membrane comprises a porous electrode substrate - to provide an electrode assembly and a polymer electrolyte fuel cell as another object. Dispersion containing the carbon short fibers (A1) and one or both surfaces of the carbon powder on the surface of the precursor sheet fiber direction is dispersed in a planar direction that is on substantially the same plane each of the fibers (C) and a fluorine-based resin by applying a liquid, the precursor the fluorine process resin was unevenly distributed in the fluorine resin localized precursor sheet containing one or both sides of the vicinity of the surface layer to said carbon powder sheet (C) (1) and , the fluorine process for producing a resin ubiquitous precursor sheet heat treating at a temperature below 400 ° C. 0.99 ° C. or higher (2) and the porous electrode substrate having after the step (1), manufactured by the manufacturing method and a solid polymer electrolyte fuel cell using porous electrode substrate and it.