TECHNOLOGY FOCUS - POLYMERS - Preferred Film: The compounds contained in hydrocarbon-type polymer electrolyte film are phosphorus acid ester antioxidant and/or thioether-type antioxidant. The content of the compounds contained in the polymer electrolyte film or electrode catalyst layer with respect to proton-conductive polymer is 0.1-5 wt.%. The polymer electrolyte film mainly consists of aromatic proton-conductive polymer. The hydrocarbon-type proton-conductive polymer is included in at least one of electrode catalyst layer. Preferred Polymer: The hydrocarbon-type proton-conductive polymer contains a sulfonic acid group, and is chosen from polysulfone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyphenylene sulfide sulfone and polyether ketone. The hydrocarbon-type proton-conductive polymer is of formula (1), formula (3): -(Ar1-Z3-Ar'-Z3)-, or formula (11 or 12).X=-S(=O)2- group or -C(=O)- group, preferably -S(=O)2- group;Z1,Z3,Z5,Z6=O or S atom, preferably oxygen atom;Ar,Ar'=bivalent aromatic group, preferably group of formula (2), more preferably group of formulae (9A-9G) or group of formula (10), and most preferably group of formula (10);R=1-4C alkyl;r=0-2;Z2=oxygen atom, sulfur atom, -C(CH3)2- group, -C(CF3)2- group, -CH2- group or cylcohexyl group, preferably oxygen atom;n1=greater than or equal to0, preferably 3 or more, and more preferably 1;Y=H or monovalent cation, preferably H;andAr1,Ar2=bivalent aromatic group, preferably group of formulae (5-8), and more preferably group of formula (8).Preferred Properties: The proton-conductive polymer satisfies a relation: 0.1less than or equal to(n3/(n3+n4))less than or equal to0.8, where n3 is mol% of structural unit (1) and n4 is mol% of structural unit (3). The proton-conductive polymer further satisfies relations: 0.9less than or equal to(n5+n6+n7+n8)/ (n5+n6+n7+n8+n9)less than or equal to1, 0.3less than or equal to(n5+n6)/ (n5+n6+n7+n8)less than or equal to0.7 and 0.01less than or equal to(n6+n8)/ (n5+n6+n7+n8)less than or equal to0.95, where n5 is mol% of structural unit (11), n6 is mol% of structural unit (1) in which Ar is group of formula (2), n7 is mol% of structural unit (12), n8 is mol% of structural unit (3) in which Ar' is group of formula (2), and n9 is mol% of other repeating structure.