PURPOSE: To uniformize plasma treatment regardless of the position of an electrode and to enhance distribution in a lot by grouping an electrode plate group and performing discharge between the opposed electrode plates in every group.

CONSTITUTION: A plurality of electrode plates 12, 12 are vertically arranged at the nearly equiintervals in a reaction chamber 11. The independent feeders 14, 14 are connected with the electrode plates 12, 12 and taken out to the outside of the chamber 11. The output of a high-frequency oscillator 15 provided to the outside of the chamber 11 is led to the chamber 11 side via a matching circuit 16. The output of the matching circuit 16 is connected with the feeder 14 taken out to the outside of the chamber 11 via a changeover switch 17. The high-frequency electric power of the oscillator 15 is successively impressed to the electrode plates 12, 12 in every group by changeover of a switching circuit 17. Thereby the film having nearly constant growing velocity and refractive index can be grown regardless of the position of the electrode 12.