TECHNOLOGY FOCUS - POLYMERS - Preparation: No general preparation given. Preferred Polymer: The sulfonic acid group-containing polymer having branched structure formed by connecting sulfonic acid group-containing structural unit of formula (16) by one or more types of phenyl-containing group of formulae (9-15). The polymer contains terminal hydroxy compound of formula (17) as portion of monomer component.X,Y'=same as defined above;Ar4=group chosen from group of formulae (3-6);Ar5=group chosen from group of formulae (3-8);q=4 or more;r,s=1 or more;andt=0 or more.Preferred Composition: The sulfonic acid group content of polymer is 0.3-5 meq/g. The ratio of number of moles of group(s) (9-15) with respect to number of moles of structural unit (1) is more than 0.7 and 0.2 or less. The ratio of number of moles of group(s) (9-15) with respect to number of moles of group (2) is more than 0.7 and 0.2 or less. Preferred Definitions:    n+m+o+p=10 or more;    (n+m)/(n+m+o+p)=0.05-0.7;    (m+p)/(n+m+o+p)=0.01-0.95;    Z3=sulfur atom;    Z1,Z2=oxygen atom;and    Ar1=group of formula (6).    EXAMPLE - 3,3'-Disulfonic acid sodium 4,4'-dichlorodiphenyl sulfone (in g) (30), 2,6-dichloro benzonitrile (42.02), bis(4-hydroxyphenyl) sulfide (55.54), 4,4'-dihydroxy biphenyl (13.27) and potassium carbonate (50.55) were added to flask and nitrogen was poured. N-methyl-2-pyrrolidone (400 mL) was added and stirred at 150 degrees C for 30 minutes. The temperature was raised to 195-200 degrees C and reacted for 12 hours. The reaction solution of cooled and stirred for 10 hours, and 1,1,1-tris(4-hydroxyphenyl) ethane (2.08) was added. The temperature was raised again and further reacted for 12 hours. Precipitation was carried out and precipitate was washed with water and dried at 110 degrees C. Sulfonic acid group-containing polymer having logarithmic viscosity of 1.57 dL/g. The polymer (10) was dissolved in N-methyl-2-pyrrolidone (30 mL) and solution was casted on hot plate top glass panel having thickness of 400 mu m and heated at 80 degrees C, 120 degrees C and 150 degrees C each for 30 minutes. The glass panel was immersed in water and film was peeled. The obtained film was immersed in pure water at room temperature and in sulfuric acid aqueous solution with concentration of 2 mol/L for 1 hour. The film was washed with water, interposed into filter paper and glass panel, stood, dried and load was applied. A polymer electrolyte membrane was manufactured.