TECHNOLOGY FOCUS - POLYMERS - Preferred Polymer: The proton-conductive polymer has an aromatic ring in the principal chain, and a proton-exchange group directly bonded to the aromatic ring or a proton-exchange group indirectly bonded through other atoms or atom groups. The polymer has a side chain having an aromatic ring. The aromatic ring or principal chain and/or aromatic ring of side chain have proton-exchange group directly bonded to the aromatic ring. The proton-exchange group is sulfonic acid group. The polymer consists of proton-exchange-group-containing aromatic repeating units of formulae: -(-Ar1-Z-Ar2-X-)-, -(-Ar3-Z'-Ar4-X'-Ar5-(-Y'-Ar6-)p-X'-)-, -(-(-Ar7-)q-X"-(-Ar8-)r-X"-)-, and -(-Ar9-)-, and aromatic repeating units not containing proton-exchange group, of formulae: -(-Ar11-Z-Ar12-X-)-, -(-Ar13-Z'-Ar14-X'-Ar15-(-Y'-Ar16-)p-X'-)-, -(-(-Ar17-)q-X"-(-Ar18-)r-X"-)-, and -(-Ar19-)-.Ar1-Ar9=bivalent aromatic group having aromatic ring in principal chain and optionally side chain having aromatic ring;Z,Z'=CO or SO2;X,X',X"=O or S;Y'=direct bond or optionally substituted methylene;p=0, 1 or 2;q,r=1, 2 or 3;andAr11-Ar19=bivalent aromatic group optionally having substituent as side chain.The polymer is a block copolymer consisting of block (A) having proton-exchange group and block (B) not having proton-exchange group. Block (A) has aromatic repeating unit of formula: -(-Ar9-)m-, and block (B) has aromatic repeating units of formulae: -(-Ar11-Z-Ar12-X-)n-, -(-Ar13-Z'-Ar14-X'-Ar15-(-Y'-Ar16-)p-X'-)n-, and -(-(-Ar17-)q-X"-(-Ar18-)r-X"-)n-.Ar9=bivalent aromatic group optionally substituted by fluorine, optionally substituted 1-10C alkyl, 1-10C alkoxy, 6-18C aryl, 6-18C aryloxy, or 2-20C acyl;n,m=5 or more;andAr11-Ar18=bivalent aromatic group optionally substituted by 1-18C alkyl, 1-10C alkoxy, 6-10C aryl, 6-18C aryloxy, or 2-20C acyl.Preferred Properties: The water contact angle of either surface of the polyelectrolyte membrane is 10-60degrees . The polyelectrolyte membrane is a hydrocarbon-type polyelectrolyte film. The polyelectrolyte membrane has micro phase-separation structure of 2 or more phases, in which a phase is with high density of block (A) and another phase is with high density of block (B). The membrane is not surface-treated on both surfaces. Preferred Process: The polyelectrolyte membrane is obtained by forming a film using a polymeric electrolytic solution obtained by dissolving a polyelectrolyte in a solvent, on a continuous support base material by solution casing method. The surface of the base material has a metal layer or a metal oxide layer, and is roll-like.