To improve the electron conductivity of an electrode and to improve the energy efficiency and operational voltage characteristics of a water electrolytic cell and a fuel cell which use the electrode by making an electron conductive substance carry on the inner surface of porous of the porous composite electrode containing a solid polymer electrolyte and catalyst particles.

Paste prepared by kneading a solid polymer electrolyte soln. such as an ion exchange resin and catalyst particles such as metals is formed into a film on a polymer film and then, naturally dried to obtain a porous solid polymer electrolytecatalyst composite electrode. This electrode consists of the solid polymer electrolyte 2 formed by three-dimensionally distributing the catalyst particles 3 and further, has lots of pores 4. An electron conductive substance 1 such as platinum group metals is made to carry on the inner surface of the pores in the electrode and if necessary, also on the electrode surface. The carrying process can be carried out, for example, by adsorbing the ions of the metals to the solid polymer electrolyte and reducing the ions. By abutting a feeder or gas diffusion layer electric collector on the both. electrode surface, a water electrolytic cell or a fuel cell of high efficiency can be formed.