PURPOSE: To form a film having good adherability and durability, by depositing an inorg. film on the surface of a transparent plastic substrate such as a lens under reduced pressure and high-frequency discharge.

CONSTITUTION: A transparent plastic substrate 6 such as a lens made of diethylene glycol bis(allyl carbonate) and an inorg. matter-evaporation source 2 such as Al2O3 or ZrO2 are placed in a vacuum chamber 1. An inert gas such as argon is introduced into the chamber 1 to control gas pressure within the chamber to 10-3W10-5Torr. Then high-frequency power is applied to ab RF coil 4 to start high-frequency discharge. The evaporation source 2 is evaporated by heating it with electron beam o form an inorg. film on the surface of the substrate 6.