NOVELTY - A gas-separation membrane has sequential lamination of porous layer (a) (1), layer (b) (2) which is a separation active layer containing compound which is capable of interacting with acidic gas, and layer (c) (3) containing crosslinked polymer having gas permeability. The layer (b) contains hydrophilic crosslinked polymer having repeating unit(s) chosen from polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone, polyethylene imine and polyallyl amine.    USE - Gas-separation membrane is used for module for gas-permeation apparatus for separating acidic gas e.g. carbon dioxide, hydrogen sulfide, carbonyl sulfide, sulfur oxide and nitrogen oxide (all claimed).    ADVANTAGE - The gas-separation membrane has excellent gas permeability, flexibility, separation selectivity and mechanical property.    DETAILED DESCRIPTION - A gas-separation membrane has sequential lamination of porous layer (a), layer (b) which is a separation active layer containing compound which is capable of interacting with acidic gas, and has molecular weight of 15000 or less, and layer (c) containing crosslinked polymer having gas permeability. The layer (b) contains hydrophilic crosslinked polymer having repeating unit(s) chosen from polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone, polyethylene imine and polyallyl amine. The crosslinked polymer contained in layer (c) contains repeating unit chosen from polyethylene glycol, polypropylene glycol, polysiloxane and polyolefin. INDEPENDENT CLAIMS are included for the following:    (1) separation of gas mixture, which involves separating acidic gas chosen from carbon dioxide, hydrogen sulfide, carbonyl sulfide, sulfur oxide and nitrogen oxide, from the gas mixture containing acidic gas and non-acidic gas containing hydrogen, methane, nitrogen and/or carbon monoxide using gas-separation membrane; and    (2) manufacture of gas-separation membrane, which involves irradiating actinic radiation to the thermosetting composition containing monomer of crosslinked polymer of layer (C) or crosslinked polymer.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the gas-separation membrane.    Layers (1,2,3)    Hydrophobic porous layer (11)    Hydrophilic porous layer (12)