The present invention addresses the problem of providing a crosslinked film and a hydrocarbon-based proton conducting solid electrolyte having a proton conductivity equal to that of a perfluorosulfonate ion exchange polymer. Disclosed as a means for solving this problem is a proton conducting polymer electrolyte which is composed of a sulfonated polyphenyl compound having a plurality of repeating units, and wherein two or more (for example, four or six) sulfonic groups are introduced into one repeating unit on average. The sulfonated polyphenyl compound may be a polymer or copolymer having a skeleton structure selected from among a polyaryl sulfide, a polyaryl ether, a polyarylsulfone, a polyarylketone and a polyaryl hexafluoroisopropylidene. A proton conducting solid polymer electrolyte membrane is able to be produced by shaping this proton conducting polymer electrolyte into a film form and crosslinking this proton conducting polymer electrolyte via sulfonic groups.