TECHNOLOGY FOCUS - ELECTRONICS - Preferred Process: The fuel cell is formed by carrying out two or more laminations of a separator which supports reaction pole supporting both sides of solid polymer electrolyte consisting of ion conductive film.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Process: The ionic conductive electrolyte film containing cation exchange membrane is impregnated in lithium salt solution to substitute ion, coupled with ion exchange group and to obtain lithium ion-substituted ionic conductive electrolyte film. Preferred Property: The relaxation time of lithium ion substituted ionic conductive electrolyte film is 2 seconds or more as measured by lithium-nuclear magnetic resonance.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The crosslinking agent is ethylene glycol dimethacrylate, ethylene glycol divinyl ether or 1,6-hexanediol divinyl ether. The volume mix ratio of crosslinking agent and styrene is 0.03-0.18 when crosslinking agent is ethylene glycol dimethacrylate or ethylene glycol divinyl ether. The volume mix ratio of crosslinking agent and styrene is less than 0.05 when crosslinking agent is 1,6-hexanediol divinyl ether. Preferred Film: The resin thin film is ethylene tetrafluoro ethylene copolymer or polyvinylidene fluoride. EXAMPLE - The resin thin film having thickness of 50 microns and containing ethylene tetrafluoro ethylene copolymer was irradiated with 400 kGy of electron beam of 250 kV. The irradiated resin film was immersed in a mixture of ethylene glycol dimethacrylate and styrene taken in a volume ratio of 2/3, and deaerated for 30 minuets. Then, polymerization was carried out at 70degreesC for 3 hours to obtain polymer which was boiled for 3 hours, polymerized in chloroform and extract-removed. Chloroform was dried and the polymer was sulfonated by immersing in chlorosulfonic acid for 24 hours to obtain ionic conductive film. The obtained ionic conductive film had favorable strength and flexibility, relaxation time of 1.4 seconds, ionic conductivity of 0.005 S/comprising and actual ionic conductivity of 0.15 S/cm.