A method of manufacturing a reverse osmosis composite membrane, including: (i) bringing a mixed liquid containing carbon nanotubes, water, and an amine component into contact with a porous support, the mixed liquid being produced through a step of pressurizing and compressing an aqueous solution containing the carbon nanotubes while flowing the aqueous solution, followed by releasing or reducing a pressure to return a volume of the aqueous solution to an original volume to mix the carbon nanotubes; and then (ii) subjecting the amine component in the mixed liquid adhering to the porous support to a crosslinking reaction.