NOVELTY - A polymer electrolyte fuel cell comprises a membrane-form polymer electrolyte disposed with a cathode on one side and an anode on the other side. The cathode comprises a catalyst and an ion exchange resin. The ion exchange resin is made of polymer comprising a segment (A) made of polymer having sulfonic acid group and a segment (B) made of fluoropolymer without an ion exchange group (IEG).    USE - As polymer electrolyte fuel cell.    ADVANTAGE - The output of the fuel cell is increased even when used for a long time, since the ion exchange resin used in the electrode is highly gas-permeable and conductive, and has high water content.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (i) a block polymer having a molecular weight of 5 x 103 - 5 x 106 comprising segments (C') and (D), where segment (C') is made of copolymer comprising 20 mol% or less of repeating units of perfluorovinyl ether having SO2X group and repeating units of tetrafluoroethylene (TFE) and segment (D) is made of an amorphous perfluoropolymer without IEG and having alicyclic structure in its main chain;    (ii) production of an amorphous polymer comprising polymerizing monomer group (a) comprising one or more fluoromonomer, in the presence of a radical initiator and an iodine-containing fluoro-compound in a non-aqueous medium or in absence of any solvent and polymerizing another monomer group (b) comprising one or more monomers different from the monomer group (a), in the presence of a polymer and another radical initiator in a non-aqueous medium or in the absence of any solvent; and    (iii) a liquid composition comprising an organic solvent having an alcoholic hydroxyl group, and a block polymer dissolved or dispersed in the organic solvent, where the polymer comprises a segment (C'') made of copolymer comprising repeating units of perfluorovinyl ether an having SO3M group and repeating units of TFE, and a segment (D).    X = fluorine, chlorine or OM;    M = hydrogen, alkali metal or NR1R2R3R4; and    R1-R4 = hydrogen or monovalent organic group.