The gas separation membrane of the present invention provides a gas separation membrane that exhibits superior gas permeability and separation selectivity and plasticity to the extent that it can endure bending testing and has little pinholes and a method for producing the gas separation membrane. Through the gas separation membrane of the present invention, it is possible to provide a superior gas separation method, a gas separation membrane module, and a gas separation and purification apparatus including the gas separation membrane module.Through the gas separation membrane of the present invention, it is possible to provide a superior gas separation method, a gas separation membrane module, and a gas separation apparatus including the gas separation membrane module.The gas separation membrane of the present invention exhibits superior gas separation selectivity, in particular, carbon dioxide permeability, and exerts superior performance as a separation membrane of carbon dioxide/methane, carbon dioxide/hydrogen. Through the gas separation membrane and the composite membrane of the present invention, it is possible to provide a superior gas separation method, a gas separation membrane module, and a gas separation and purification apparatus including the gas separation membrane module.A gas separation membrane having a separation-active membrane containing a compound represented by the following Formula (I) having a boiling point or a decomposition temperature of 200° C. or higher and a cross-linked polymer having a dissociable group and a repeating unit derived from alkylene glycol, wherein the gas separation membrane separates at least one acid gas from a gas mixture containing the at least one acid gas and at least one non-acid gas.