Gas separation membrane

A gas separation membrane that separates, by selective transmission, carbon dioxide from a mixed gas containing the carbon dioxide and nitrogen, the gas separation membrane comprising:

• a first layer, wherein the first layer includes an organopolysiloxane;
• and
• a second layer provided at one surface of the first layer and composed of a compound having carbon dioxide separation ability, wherein
• the compound of the second layer includes one of:
• a structure derived from one of polyethylene terephthalate, polyacetal polylactic acid, cellulose, a cellulose derivative, lignin, or a coupling agent, or
• a polydimethylsiloxane derivative,
• an average thickness of the second layer is smaller than an average thickness of the first layer, and
• the second layer satisfies 0.56<ξ2, where an activity coefficient of nitrogen in the second layer, calculated by a COSMO-RS method, is γ2N2, an activity coefficient of carbon dioxide in the second layer is γ2CO2, and a separation performance parameter of the second layer at 25° C. is ξ2=ln(γ2N2)−ln(γ2CO2).