TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Compound: The catalyst precursor compound is a compound having platinum group metal.    TECHNOLOGY FOCUS - POLYMERS - Preferred Method: An electrode precursor layer is formed on a base material using an electrode formation paste composition containing polyarylene polymer electrolyte, adsorbing catalyst precursor compound by electrode precursor layer, chemically reducing the precursor compound, and forming composite electrode. Alternately, the catalyst precursor compound contained in the paste composition consisting of the polyarylene-type polymer electrolyte and catalyst precursor compound, is chemically reduced and catalyst substance is produced. The composition containing the catalyst substance is applied on a base material, electrode layer is produced, and composite electrode is obtained. Preferred Electrolyte: The polyarylene-type polymer electrolyte consists of polyarylene having sulfonic acid group, and has structural units of formulae (1,2).Y=-CO-, -SO2-, -SO-, -CONH-, -COO-, -(CF2)i-, or -C(CF3)2-;i=1-10;Z=direct bond, -O-, -S-, -(CH2)j-, or -C(CH3)2-;j=1-10;Ar=-SO3H, -O(CH2)pSO3H, -O(CF2)pSO3H, or aromatic group having substituent;p=1-12;m,n=0-10;k=1-4;A,D=-CO-, -SO2-, -SO-, -CONH-, -COO-, -(CF2)i-,-(CH2)j-, -CR'2-, cyclohexylidene, fluorenylidene, -O-, or -S-;R'=aliphatic hydrocarbon, aromatic hydrocarbon or halogenated hydrocarbon;B=oxygen atom or sulfur atom;R1-R16=H, fluorine atom, alkyl, halogenated alkyl, partially or wholly halogenated (allyl, aryl, nitro or nitrile);s,t=0-4;andr=0 or 1.Preferred Film: The proton conductive film consists of polyarylene-type polymer electrolyte, and used as base material. EXAMPLE - 10 wt.% N-methyl-2-pyrrolidone solution of sulfonated polyarylene of formula (II) was cast on a glass plate, dried and proton conductive film having film thickness of 40 microns was produced. An electrode formation paste was prepared by mixing and stirring a polymer solution containing sulfonated polyarylene of formula (II) dissolved in N-methyl-2-pyrrolidone, with Vulcan XC-72 (RTM: carbon particles) in the mix ratio of 0.9:1. The obtained paste was applied on the tetrafluoroethylene-hexafluoro propylene copolymer sheet, and electrode precursor sheet was produced. The precursor sheet was immersed in aqoues solution of platinum ammonium chloride ((Pt(NH3)4)Cl2). The sheet was removed, washed with deionized water, and dried at 50degreesC in air. The sheet was then reduced in hydrogen atmosphere for 7 hours, washed with nitric acid and deionized water, dried at 50degreesC and polyelectrolyte-catalyst composite electrode layer was produced. The composite electrode layer had platinum content of 0.1 mg/cm2.