Mixture separation membrane, method for altering composition of mixture using same, and mixture separation device

Disclosed is a mixture separation membrane that can alter the composition of a mixture that contains aromatic hydrocarbons and non-aromatic hydrocarbons by means of permeating the aforementioned mixture through said membrane, which contains at least 50% carbon by mass, and which has a transmission rate of SF 6 gas at room temperature before permeation of the aforementioned mixture of at least 1.0x10 -8 mol/Pa·m 2 ·s and less than 4.1x10 -6 mol/Pa·m 2 ·s.