TECHNOLOGY FOCUS - ELECTRONICS - Preferred Cell: The solid electrolyte is in the form of a film, and the fuel cell further comprises a pair of gas-impermeable separators arranged to sandwich the gas diffusion electrode; and a pair of current collectors arranged between the solid electrolyte and the separator. Preferred Components: The gas diffusion electrode is an electrode in which a fine particle of catalyst metal (12b, 13b) carried on the surface of a conductive material composed of carbon material (12a, 13a) by a binder, where the binder comprises the solid electrolyte.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The sulfonic acid group bonding to the aromatic ring via the linking group containing a sulfur atom is represented by the formula -B1-(X-B2)m1-SO3M (I). The main chain comprises at least one type of repeating unit of formula -R1-X1 and, (I) bonds to the aromatic ring contained in the main chain.B1 and B2=a linking group (preferably a linking group having 0 - 100 carbon atoms selected from an alkylene, arylene, alkenylene, alkynylene, amide, ester, sulfonamide, sulfonic acid ester, ureido, sulfonyl, sulfinyl, thioether, ether, carbonyl, and/or heteryllene group);X=a group containing a sulfur atom (preferably S, SO or SO2);M=cation;m1=greater than or equal to1 (preferably 1 - 6);R1=benzene-1,4-di-yl (substituted at 2,3, 5 and 6th positions by S1 - S4 respectively), benzene-1,3-di-yl (substituted at 2, 4, 5 and 6th positions by S5 - S8 respectively), benzene-1,2-di-yl (substituted at 3 - 6th positions by S9 - S12 respectively), biphenyl-di-yl, tri-phenyl-di-yl, naphthalene-di-yl, anthracene-di-yl, anthracene-9,10-di-yl, phenanthrene-di-yl, diphenylcyclohexylmethane-di-yl, triphenylmethane-di-yl, tetraphenyl-di-yl, 9,9-diphenyl-9H-fluorene-di-yl, 1,2,4,5-tetraphenyl-benzene-3,6-di-yl, 2,3,5,2',3',5'-hexaphenyl-biphenyl-4,4'-di-yl, furan-di-yl, thiophene-di-yl, dibenzofuran-di-yl, 9H-fluorene-di-yl, fluoren-9-one-di-yl, or 9H-carbazole-di-yl;S1- S12=H or a substitution group;X1=single bond, C(R5R6), O, S, CO, SO and/or SO2;andR5 and R6=H, alkyl, alkenyl, aryl or halogen-substituted alkyl group. EXAMPLE - 2,2-Bis(4-hydroxyphenyl)propane (22.8 g), bis(4-chlorophenyl)sulfone (28.7 g), potassium carbonate (17.25 g), dimethylacetamide (DMAc) (150 ml), toluene (75 ml) were mixed. The mixture was refluxed for 6 hours under nitrogen atmosphere, and surplus toluene was removed. The reaction mixture was heated at 160degreesC for 10 - 12 hours. The resulting viscous solution was cooled to 100degreesC, to which chlorobenzene (75 ml) was added. After work-up, a polysulfone was obtained. Chloromethylmethyl ether (18.75 ml), to which tin tetrachloride (0.15 ml) had been added, was added to a solution prepared by dissolving (at 60degreesC) polysulfone (11 g) in 1,1,2,2-tetrachloroethane (200 ml). The solution was stirred at 110degreesC for 3 hours under nitrogen substitution to be reacted. Methanol (3 ml) was added, and the solution was cooled to room temperature. Methanol (400 ml) was added and after work-up, a chloromethylated polysulfone (9.3 g) were obtained. Potassium-tert-butoxide (4.6 g) and sodium 3-mercapto-1-propane sulfonate (6.6 g) were mixed, to which dewatered dimethylformamide (100 ml) was added. The solution was stirred at 80degreesC for 10 minutes under nitrogen flow. A solution prepared by dissolving chloromethylated polysulfone (5 g) in dewatered DMF (100 ml) was added to the solution. The solution was stirred at 80degreesC for 5 hours under nitrogen flow to allow it to react. After work-up, a polymer (4.8 g) having been introduced with a sulfonic acid group was obtained. The polymer (5 g) was dissolved in dimethylformamide (40 ml) to prepare a dope liquid. The dope liquid was poured on a glass plate and expanded using a bar coater. Then, it was dried at 65degreesC for 15 hours. The film was stripped from the glass plate, dipped in hydrochloric acid (1 mol/l HCl) overnight to carry out salt exchange to give a sulfonated polysulfone film (solid electrolyte film) (test). A polysulfone was sulfonated with concentrated sulfuric acid to give a polymer having been introduced with a sulfonic acid group in a biphenyl unit. The obtained sulfonated polymer was film-formed by a cast method in the same way as in test to give a sulfonated polysulfone film (solid electrolyte film) (control). A fuel cell was made by using test or control electrolyte film. The test/control cell showed a Tg (degreesC): storage elastic modulus (Gpa): oxygen permeability (mol/cm.sec): proton conductivity (S/cm): cell voltage (V) of 199/207: 1.9/1.9:1.49x10-11/3.44x10-12: 0.23/0.16: 0.65/0.51 respectively.