A discharge electrode E in an electrode chamber C is formed of a pair of electrode members 8 and 9 having lengths equal to or greater than a width of a film F. Also, the pair of electrode members 8 and 9 are disposed facing each other so as to sandwich a support member 4 there-between, which has nearly the same length as to electrode members; a gap is formed in a section in which the pair of electrode members 8 and 9 face each other; and this gap is open at a tip of the discharge electrode so as to serve as a gas pathway 15. Meanwhile, in the aforementioned support member 4, a plurality of gas guiding holes 5 are formed in a longitudinal direction thereof, and the gas guiding holes are in communication with a gas supplying system.