Patent ID: 8418650

Claim:
An inner electrode for barrier film formation that is inserted inside a plastic container having an opening, supplies a medium gas to the inside of the plastic container, and supplies high frequency power to an outer electrode arranged outside the plastic container, thereby generating discharge plasma on the inner surface of the plastic container to form a barrier film on the inner surface of the plastic container, the inner electrode for barrier film formation comprising: a gas supply pipe having a gas flow path to supply the medium gas; and an insulating member that includes a gas outlet communicated with an end portion of the gas supply pipe, and a falling-off preventing structure that screws into or engages with the end portion of the gas supply pipe, wherein the falling-off preventing structure of the insulating member includes: threads formed on the insulating member, the threads screwed into a threaded part of the gas supply line; the gas supply pipe having the gas flow path to supply the medium gas and the end portion thereof is provided with a concave portion having a long space in the axial direction; and a solid cap member having a gas outlet and threads on an outer surface, the threads being screwed on an inner surface of the concave portion of the gas supply pipe, the gas outlet being communicated with the gas flow path, the solid cap member being screwed, in a screw portion, into the concave portion such that the side faces become flush with each other, the solid cap member being formed with a hole over the axial direction and fitted with the outer periphery of the gas outlet of the insulating member.