According to the invention, a chemically adsorbing material is reacted with a substrate surface having active hydrogen groups by dipping the substrate into a solution of the chemically adsorbing material simultaneous and applying ultrasonic waves to the solution. In this way, a high concentration monomolecular and/or polymer film substantially free from pin holes can be formed in a short period of time. That is, while the ultrasonic waves are applied, a chemical adsorbing material having an end functional chlorosilyl group is adsorbed onto the substrate surface, thereby forming a chemically adsorbed monomolecular and/or polymer film. The frequency of the ultrasonic waves are suitably in a range of 25 to 50 kHz. In addition, after formation of the adsorbed film, the substrate is washed for making monomolecular film by dipping it in a washing solution while applying ultrasonic waves. In this way, non-reacted chemical adsorbing material remaining on the substrate can be efficiently washed away.