Coating a hydrogel-state coating liquid containing at least a hydrophilic compound and an acid gas carrier on one surface of a hydrophobic porous body having three-dimensional network structure formed through intersecting, coupling or branching of a plurality of fibrils, and a large number of pores formed of microscopic interstices divided by the plurality of fibrils to form a facilitated transport membrane thereon. The hydrophobic porous body has an average inter-fibril distance of 0.001 μm or more and 2 μm or less inside a plane in parallel to a surface on which the acid gas separation facilitated transport membrane is formed, an average fibril length of 0.01 μm or more and 2 μm or less inside the plane, and an average inter-fibril distance of 0.001 μm or more and 2 μm or less in a direction perpendicular to the surface.