An oxidized polymer being an oxide of a polymer built up from either a single structure or a mixed structure of a structural unit represented by the following chemical formula: and a structural unit represented by the following chemical formula: wherein X 1 and X 2 may be the same as or different from each other, wherein X 1 and X 2 represent: H; an alkyl group having 1 to 12 carbon atoms, optionally having a substituent; an alkoxy group having 1 to 12 carbon atoms, optionally having a substituent; an alkylene oxide group having 1 to 12 carbon atoms, optionally having a substituent; a thiocyano group optionally having a substituent; an amino group optionally having a substituent; or a thioalkyl group optionally having a substituent, or X 1 and X 2 are combined to be an alkylenedioxy group having 1 to 12 carbon atoms and being directly linked via the oxygen atoms to the thiophene moiety, optionally having a substituent, or an alkylenedithio group having 1 to 12 carbon atoms and being directly linked via the sulfur atoms to the thiophene moiety, optionally having a substituent, wherein said optional substituents are selected from the group consisting of a straight chain, branched or cyclic alkyl group having 1 to 12 carbon atoms, a sulfo group, a hydroxyl group, a carboxyl group having 1 to 12 carbon atoms, an amino group, an amide group having 1 to 12 carbon atoms, an ester group having 1 to 12 carbon atoms, and a straight chain, branched or cyclic alkyl group having 1 to 12 carbon atoms, alkoxy alkyl group having 1 to 12 carbon atoms, and alkylene oxide group having up to 12 carbon atoms, wherein X 1 and X 2 are not any of combinations of both X 1 and X 2 being H, of both X 1 and X 2 being the alkyl group having 1 to 12 carbon atoms, and of one of X 1 and X 2 being H with the other being the alkyl group having 1 to 12 carbon atoms, and wherein R represents a phenyl group having an acidic substituent or a salt thereof, wherein the acidic substituent or the salt thereof is a sulfo group or an alkali metal salt thereof, or a phosphoric acid group or an alkali metal salt thereof, and wherein the oxidized polymer is a self-doped polymer. wherein X 1 and X 2 may be the same as or different from each other, wherein X 1 and X 2 represent: H; an alkyl group having 1 to 12 carbon atoms, optionally having a substituent; an alkoxy group having 1 to 12 carbon atoms, optionally having a substituent; an alkylene oxide group having 1 to 12 carbon atoms, optionally having a substituent; a thiocyano group optionally having a substituent; an amino group optionally having a substituent; or a thioalkyl group optionally having a substituent, or H; an alkyl group having 1 to 12 carbon atoms, optionally having a substituent; an alkoxy group having 1 to 12 carbon atoms, optionally having a substituent; an alkylene oxide group having 1 to 12 carbon atoms, optionally having a substituent; a thiocyano group optionally having a substituent; an amino group optionally having a substituent; or a thioalkyl group optionally having a substituent, or X 1 and X 2 are combined to be an alkylenedioxy group having 1 to 12 carbon atoms and being directly linked via the oxygen atoms to the thiophene moiety, optionally having a substituent, or an alkylenedithio group having 1 to 12 carbon atoms and being directly linked via the sulfur atoms to the thiophene moiety, optionally having a substituent, wherein said optional substituents are selected from the group consisting of a straight chain, branched or cyclic alkyl group having 1 to 12 carbon atoms, a sulfo group, a hydroxyl group, a carboxyl group having 1 to 12 carbon atoms, an amino group, an amide group having 1 to 12 carbon atoms, an ester group having 1 to 12 carbon atoms, and a straight chain, branched or cyclic alkyl group having 1 to 12 carbon atoms, alkoxy alkyl group having 1 to 12 carbon atoms, and alkylene oxide group having up to 12 carbon atoms, wherein X 1 and X 2 are not any of combinations of both X 1 and X 2 being H, of both X 1 and X 2 being the alkyl group having 1 to 12 carbon atoms, and of one of X 1 and X 2 being H with the other being the alkyl group having 1 to 12 carbon atoms, and wherein R represents a phenyl group having an acidic substituent or a salt thereof, wherein the acidic substituent or the salt thereof is a sulfo group or an alkali metal salt thereof, or a phosphoric acid group or an alkali metal salt thereof, and wherein the oxidized polymer is a self-doped polymer.