PURPOSE: To equalize various characteristics of a film formed, the quality of the film and film thickness, and to shape the film having a large area by gradually increasing the sectional area of gas transport space between film formation space and gas exciting space toward the film formation space.

CONSTITUTION: The sectional area of gas transport space between film formation space 5 and exciting space 3 is expanded gradually toward the film formation space 5. A raw material gas 1 is excited by microwaves 2 in the exciting space 3, and one part is deposited onto a base body 6 mounted into the film formation space 5 through a hone-shaped nozzle 4 made of a metal, and one part is exhausted 7 by an exhaust means. When the raw material gas 1 is excited by microwaves and brought to the state of plasma, partial microwaves are emitted from a cavity resonator 8, but they are damped slowly by the hone-shaped nozzle 4 made of the metal, and do not intrude into the cavity resonator again, thus allowing plasma discharge even at low voltage. Since length l1 up to the film formation space from the exciting space is made sufficiently long, plasma does not reach onto the base body.