A bischloroformate composition that is represented by a formula below, comprises a plurality of Ar components, and has an average number of monomer units, which is calculated by an expression (Numerical Expression 1) below, ranging from 1.0 to 1.99, wherein the plurality of Ar components each independently comprise Ar 1 or Ar 2, the plurality of Ar components comprise at least one Ar 1 and at least one Ar 2, Ar 1 is a group represented by a formula below and Ar 2 is a group represented by a formula below, and a molar composition ratio represented by Ar 1 / (Ar 1 + Ar 2) ranges from 45 mol% to 99 mol%, where Ar is the group represented by the formula below or the formula below and m1 represents the average number of monomer units of the bischloroformate composition, where: R 1 and R 2 in the formula are each independently a hydrogen atom or a substituent, R 1 and R 2 as substituents being each independently selected from the group consisting of a trifluoromethyl group and an alkyl group having 1 to 3 carbon atoms; X in the formula is selected from the group consisting of -O-, -CO-, -S-, -SO 2 -, -CR 5 R 6 -, a substituted or unsubstituted cycloalkylidene group having 5 to 12 carbon atoms, a substituted or unsubstituted adamantane-2,2-diyl group, a substituted or unsubstituted adamantane-1,3-diyl group, a substituted or unsubstituted α,ω-alkylene group having 2 to 12 carbon atoms, a 9,9-fluorenylidene group, a 1,8-menthanediyl group, a 2,8-menthanediyl group, and a group represented by a formula below; R 5 and R 6 are each independently a hydrogen atom or a substituent, R 5 and R 6 as substituents being each independently selected from the group consisting of an alkyl group having 1 to 5 carbon atoms, a trifluoromethyl group, and a substituted or unsubstituted aryl group having 6 to 12 carbon atoms; and R 3 and R 4 in the formula are each independently selected from the group consisting of a perfluoroalkyl group having 1 to 3 carbon atoms and an alkyl group having 1 to 3 carbon atoms, where R are each independently an aliphatic hydrocarbon group having 1 to 6 carbon atoms, [Numerical Expression 1] average number of monomer units m 1 = 1 + Mav − M 1 / M 2 where: Mav represents (2 × 1000 / (CF number)); M1 represents an average molecular weight of a bischloroformate compound present at the ratio represented by Ar 1 / (Ar 1 + Ar 2) in the bischloroformate composition with the average number of monomer units being 1.0; M2 represents (M1 - Y); the CF number [a mole number of a chlorine atom/kg] is (CF value / concentration) of a bischloroformate composition solution produced by fully dissolving the bischloroformate composition in an organic solvent; the CF value is the mole number of the chlorine atom in the bischloroformate compound contained in 1 L of the bischloroformate composition solution; the concentration [kg/L] is an amount of a solid content obtained by condensing 1 L of the bischloroformate composition solution; and Y is a total atom weight of two chlorine atoms, one oxygen atom and one carbon atom which are desorbed at polycondensation of the bischloroformate compound and a phenol compound. R 1 and R 2 in the formula are each independently a hydrogen atom or a substituent, R 1 and R 2 as substituents being each independently selected from the group consisting of a trifluoromethyl group and an alkyl group having 1 to 3 carbon atoms; X in the formula is selected from the group consisting of -O-, -CO-, -S-, -SO 2 -, -CR 5 R 6 -, a substituted or unsubstituted cycloalkylidene group having 5 to 12 carbon atoms, a substituted or unsubstituted adamantane-2,2-diyl group, a substituted or unsubstituted adamantane-1,3-diyl group, a substituted or unsubstituted α,ω-alkylene group having 2 to 12 carbon atoms, a 9,9-fluorenylidene group, a 1,8-menthanediyl group, a 2,8-menthanediyl group, and a group represented by a formula below; R 5 and R 6 are each independently a hydrogen atom or a substituent, R 5 and R 6 as substituents being each independently selected from the group consisting of an alkyl group having 1 to 5 carbon atoms, a trifluoromethyl group, and a substituted or unsubstituted aryl group having 6 to 12 carbon atoms; and R 3 and R 4 in the formula are each independently selected from the group consisting of a perfluoroalkyl group having 1 to 3 carbon atoms and an alkyl group having 1 to 3 carbon atoms, Mav represents (2 × 1000 / (CF number)); M1 represents an average molecular weight of a bischloroformate compound present at the ratio represented by Ar 1 / (Ar 1 + Ar 2) in the bischloroformate composition with the average number of monomer units being 1.0; M2 represents (M1 - Y); the CF number [a mole number of a chlorine atom/kg] is (CF value / concentration) of a bischloroformate composition solution produced by fully dissolving the bischloroformate composition in an organic solvent; the CF value is the mole number of the chlorine atom in the bischloroformate compound contained in 1 L of the bischloroformate composition solution; the concentration [kg/L] is an amount of a solid content obtained by condensing 1 L of the bischloroformate composition solution; and Y is a total atom weight of two chlorine atoms, one oxygen atom and one carbon atom which are desorbed at polycondensation of the bischloroformate compound and a phenol compound.