1. A gas separation membrane comprising:a gas separation layer containing a cellulose resin; and
an organopolysiloxane compound layer disposed on the gas separation layer,
wherein a 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-K? X-ray intensity after immersion in chloroform)/(Si-K? X-ray intensity before immersion in chloroform), Mathematical expression (I)
the organopolysiloxane compound layer has a structure in which organopolysiloxane compounds are linked to each other through a linking group selected from *O-M-O*, *S-M-S*, *NRaC(?O)*, *NRbC(?O)NRb*, *OCH2O*, *SCH2CH2*, *OC(?O)O*, *CH(OH)CH2OCO*, *CH(OH)CH2O*, *CH(OH)CH2S*, *CH(OH)CH2NRc*, *CH(CH2OH)CH2OCO*, *CH(CH2OH)CH2O*, *CH(CH2OH)CH2S*, *CH(CH2OH)CH2NRc*, *CH2CH2*, *C(?O)O?N+(Rd)3*, *SO3?N+(Re)3*, and *PO3H?N+(Rf)3*,
where M represents a divalent to tetravalent metal atom; Ra, Rb, Rc, Rd, Re, and Rf each independently represent a hydrogen atom or an alkyl group, the symbol * represents a linking site, the linking group *CH2CH2* is formed by a polymerization reaction of compounds having a vinyl group, and
the organopolysiloxane compound layer contains 10 to 5,000 ppm of an organic solvent.