TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The platinum ion is injected to a dose amount (phi) of 1x1012 pieces/cm2-1x1019 pieces/cm2. The surface of solid polymer electrolyte film is further injected with gases other than platinum or ion of noble gas. Preferred Method: Deterioration of platinum catalyst is suppressed by performing ion implantation by platinum, or adding and injecting metals, such as ruthenium, molybdenum, tin, manganese and iron, before and after platinum injection.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The platinum ion is injected to a dose amount (phi) of 1x1012 pieces/cm2-1x1019 pieces/cm2. The surface of solid polymer electrolyte film is further injected with gases other than platinum or ion of noble gas. Preferred Method: Deterioration of platinum catalyst is suppressed by performing ion implantation by platinum, or adding and injecting metals, such as ruthenium, molybdenum, tin, manganese and iron, before and after platinum injection.    TECHNOLOGY FOCUS - POLYMERS - Preferred Material: The polymeric material is sulfonated polyimide, sulfonated polysulfone, sulfonated polyether sulfone, sulfonated polybenzimidazole, sulfonated polyether ether ketone or sulfonated polyphenylene, preferably sulfonated polyimide. The polymeric material is a polyimide resin having structural unit of formula (1).x,y=0-100;andx/y=95/5-20/80. EXAMPLE - A sulfonic acid group-containing polyimide was prepared by using 2,2'-diamino diphenyl hexafluoro propane, 2,2'-benzidine disulfonic acid, triethylamine, m-cresol, 1,4,5,8-tetracarboxylic acid dianhydride and benzoic acid. Subsequently, the obtained polyimide (10 wt.%) was dissolved in dimethyl sulfoxide (90 wt.%), and a sulfonic acid group-containing polyimide solution was obtained. The obtained solution was cast on a glass Petri-dish. Solvent was evaporated under reduced pressure, and a film of thickness 50 microns was formed. The film was immersed in 1 N hydrochloric acid, and an electrolyte film was produced. A solid polymer electrolyte fuel cell produced using the film, had high efficiency.