An approximate solution of the facilitation factors in the facilitated transport of CO2 through a liquid membrane containing primary or secondary amine has been developed for the case where a reversible reaction, A (CO2) + 2B (amine) reversible E (carbamate) + F (protonated amine), occurs in the membrane, and the reaction rate is expressed by k1(C(A)C(B) - C(E)C(F)/K(eq)C(B))/(1 + K’/C(B)). In the present approximation method, separate constant concentrations of the carrier B and the protonated amine F are assumed at the two boundaries of the membrane for evaluating the influx and outflux of the permeant species, and these concentrations are determined so that these fluxes agree with each other in the steady state. It was confirmed that the facilitation factors calculated by the present approximation method agree with the results which had been obtained previously by numerical integration of the governing differential equations. Calculated result on the system parameter dependencies of the facilitation factor are also presented.