This carbon dioxide separation membrane includes a porous layer having affinity with ionic liquids (C), said layer holding an ionic liquid-containing liquid (A) within voids therein, and a porous layer lacking affinity with ionic liquids (B). The porous layer having affinity with ionic liquids (C) may include an inorganic material (e.g., metal oxide particles having an average particle size of approximately 0.001 to 5 μｍ on a number basis). The average thickness of the porous layer having affinity with ionic liquids (C) may be approximately 0.01 to 10 μｍ. The porous layer having affinity with ionic liquids (C) may include 0.1 to 99 volume parts of the ionic liquid-containing liquid (A) with respect to 100 volume parts of voids therein. The carbon dioxide separation membrane may be used for fertilizing plants with carbon dioxide. The carbon dioxide separation membrane allows the size of a carbon dioxide concentrating device to be reduced and allows said device to be smoothly operated.
