PROBLEM TO BE SOLVED: To provide a method for promoting the photosynthesis of photosynthetic organisms, excellent in handling properties, using a COcarrier which is high in COabsorption, and has COreleasing properties, and usable for reduction the amount of COderived from a small-scale disperse type emission source.SOLUTION: This method for promoting the photosynthesis of photosynthetic organisms includes a COabsorbing process of producing a COcarrier by making swelling gel which includes an element shown by following general formula (1) (in the formula, R shows a hydrogen atom or 1-4C alkyl group) absorb CO, and a COreleasing process of supplying to the photosynthetic organisms, COwhich the COcarrier releases at a growth temperature of the photosynthetic organisms.
