A gas separation membrane has a gas separation layer containing a cellulose resin, and an organopolysiloxane compound layer disposed on the gas separation layer in which Si ratio of the organopolysiloxane compound layer after immersion in chloroform to the organopolysiloxane compound layer before immersion in chloroform, the Si ratio being calculated by Mathematical expression (I), is 0.6 to 1.0. Si ratio=(Si—Kα X-ray intensity after immersion in chloroform)/(Si—Kα X-ray intensity before immersion in chloroform)  Mathematical expression (I)