PURPOSE: To prevent the obstruction of a monomolecular film by oxidation, by using inert gas as a gaseous phase and developing a monomolecular film to the interface of the gaseous phase and a liquid phase and transfer said monomolecular film to the surface of a carrier.

CONSTITUTION: When a low concn. solution, which was prepared by dissolving a desired film forming molecule group in a proper solvent, is dripped on the surface of a purified liquid 3 by a spuit to be developed on the surface of the liquid 3, a monomolecular film is formed on the surfaces of the liquid 3 after the solvent was volatilized. The surface density of this monomolecular film is increased by the movement of a float 4 to form a solid film which is, in turn, adhered to a desired carrier 12 by the up-and-down movement of said carrier 12 to the surface of the liquid 3. A square shaped liquid tank 1 equipped with the above mentioned various accessory devices is arranged in a hermetically closable open air blocking box 13. Nitrogen gas or argon gas is supplied into the open air blocking box 3 from a gas supply source 21 and film forming operation is performed in such a state that the interior of the open air blocking box is held under an inert atmosphere.