TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Properties: The proton conductive film has dimension swelling rate of 5% or less, when immersed in pure methanol at 25degreesC for 24 hours, and total pore volume of 0.3 cm3/g or less measured by Brunauer Emmett Teller method. The silicon-oxygen cross-linked component has condensation degree of 85% or more measured by 29Si-nuclear magnetic resonance (NMR) analysis method. The proton conductive film has a peak resulting from hydroxyl group at 3500 cm-1 vicinity, and does not have a peak resulting from methyl or methylene group at 3000 cm-1 vicinity, observed from total reflection infrared absorption measurement. Preferred Component: The surface of silicon-oxygen cross-linked structure microparticles has a sulfonic acid group, which is covalent bonded with a silicon atom through 20C or less linear alkylene group. Preferred Process: A cross-linking agent having hydrolysable silyl group and/or silanol group is filled in the pore formed between microparticles. Composite reinforcement of the proton conductive film is carried out using a polymeric material having a sulfonic acid group.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Properties: The proton conductive film has dimension swelling rate of 5% or less, when immersed in pure methanol at 25degreesC for 24 hours, and total pore volume of 0.3 cm3/g or less measured by Brunauer Emmett Teller method. The silicon-oxygen cross-linked component has condensation degree of 85% or more measured by 29Si-nuclear magnetic resonance (NMR) analysis method. The proton conductive film has a peak resulting from hydroxyl group at 3500 cm-1 vicinity, and does not have a peak resulting from methyl or methylene group at 3000 cm-1 vicinity, observed from total reflection infrared absorption measurement. Preferred Component: The surface of silicon-oxygen cross-linked structure microparticles has a sulfonic acid group, which is covalent bonded with a silicon atom through 20C or less linear alkylene group. Preferred Process: A cross-linking agent having hydrolysable silyl group and/or silanol group is filled in the pore formed between microparticles. Composite reinforcement of the proton conductive film is carried out using a polymeric material having a sulfonic acid group.    TECHNOLOGY FOCUS - POLYMERS - Preferred Material: The polymeric material consists of polyethylene or fluororesin such as polytetrafluoroethylene, and is a porous material having film thickness of 20-100 microns, pore size of 0.05-0.2 microns and porosity of 60% or more. The porous material is subjected to hydrophilization treatment. A silane coupling agent such as epoxy silane and/or amino silane, binds the proton conductive film and the hydrophilization treated porous material. The polymeric material has cross-linked structure by a metal-oxygen bond, and a hole formed in the cross-linked structure is an organic-inorganic composite material with continuous pore structure connected continuously. EXAMPLE - A mercapto group-containing silane oligomer was prepared using 3-mercapto propyl trimethoxysilane (in g) (21.2), tetra-ethoxysilane (52.5), methanol (10.7), hydrochloric acid (6.2), potassium fluoride (0.057) and diethyl ether (120 ml). Water (0.16) and triethylamine (0.06) were dripped over a mixed liquid containing the obtained oligomer (4.37) and silicone oligomer (0.51), and stirred at room temperature for 10 minutes. The resulting solution was impregnated into polytetrafluoroethylene porous membrane having film thickness of 50 microns, average pore diameter of 0.2 microns and porosity of 80%. A fluororesin film was covered on the obtained film, leveled such that film thickness became 50 microns, and cured at room temperature for 80 hours. The film was peeled, and cured at room temperature for 24 hours. The cured film was heat-hardened at 80degreesC for 24 hours, heated at 100-200degreesC for 1 hour, and baked at 200degreesC for 3 hours. The obtained film was immersed in 1N hydrochloric acid aqueous solution and water, and unreacted substance and catalyst were extracted from the film. The film was further immersed in acetic acid (125 ml) and peracetic acid (100 ml), and heated at 60degreesC for 1 hour. The film was removed from peracetic acid solution, and immersed twice in water at 80degreesC for 1 hour, to obtain a semi-transparent proton conductive film. The proton conductive film had ion exchange capacity of 0.71 meq/g, methanol permeability coefficient of 78 micronsol/cm/day, dimension swelling rate of 1.1%, pore volume of 0.059 cm3/g and condensation degree of 94%.