TECHNOLOGY FOCUS - POLYMERS - Preferred Copolymer: The structure block (A) of copolymer has proton conduction group-containing structural unit of formulae (1,2). The structure block (B) of copolymer has proton conduction group-containing structural unit of formula (2).R1=H, fluorine atom, nitrogen atom, phosphorus atom and/or oxygen atom, carbon atom and/or silicon atom, or proton conduction group;Ar1=alicyclic hydrocarbon, aromatic group and/or boron nitride group optionally having proton conduction group, and optionally substituted by fluorine or alkyl optionally substituted with fluorine;Z=group having proton conduction group, preferably of formula (3);Z'=proton conduction group;x,y=1 or more;R2=H, fluorine atom, nitrogen atom, phosphorus atom and/or oxygen atom, or carbon atom and/or silicon atom, and does not contain proton conduction group;Ar2=alicyclic hydrocarbon, aromatic group and/or boron nitride group optionally substituted by fluorine or alkyl optionally substituted with fluorine, and does not contain proton conduction groyup;E=connection portion for chemical bonding of R1,R2,Ar1,Ar2;a,b,d,e=1 or more;c,f,g=0 or more;andf+g=1 or more. EXAMPLE - 3,5-diamino benzoic acid dihydrochloride (in g) (0.25), 4,4'-oxy dianiline (0.1) and m-cresol (4 ml) were stir-dissolved under nitrogen atmosphere. 1,4,5,8-naphthalene tetracarboxylic acid dianhydride (0.43) and benzoic acid (0.3) were added, and solution was heated at 80degreesC for 4 hours. The reaction liquid was further heated at 180degreesC for 10 hours, and cooled to room temperature. 4,4'-oxy dianiline (0.1) and m-cresol (1.5 ml) were added. 1,4,5,8-naphthalene tetracarboxylic acid dianhydride (0.08) and benzoic acid (0.1) were added, and solution was heated at 80degreesC for 4 hours. The reaction liquid was further heated at 180degreesC for 10 hours, and cooled to room temperature. 2,2'-benzidine sulfonic acid dihydrochloride (0.4), m-cresol (2 ml), triethyl amine (0.3 ml) and benzoic acid (0.3) were added, and heated at 80degreesC for 4 hours. The reaction liquid was heated at 180degreesC for 10 hours, and cooled. The deposit was washed and dried to produce a film. The film was immersed in methanol, heated, and immersed in sulfuric acid aqueous solution. Proton exchange was carried out, and washed to produce solid electrolyte film. The film had ion exchange capacity of 1.81 milliequivalent/g, proton conductivity of 0.09 S/cm, methanol transmission rate of 0.36x10-6 cm2/second, and favorable water resistance.