A pressure container is filled with a base material having at least part of the surface coated with an organic matrix including at least one member selected from the specific functional groups, and a material solution containing a carbonate material as a material for carbonate film and an organic polymer including at least one member selected from the specific groups. In succession, by supplying CO.sub.2 into the pressure container at 2 atm or higher, a carbonate film is deposited on the surface of the organic matrix.