The present invention is intended to effectively inhibit detachment of a vapor-deposited film formed on the external surface of gas supply pipe and to minimize sticking of any detached vapor-deposited film to the internal surface of vessel and to the surface of nozzle seal. There is provided gas supply pipe (4) for plasma treatment adapted to be inserted in the interior of vessel (3) held within plasma treatment chamber (1) and to supply a gas for plasma treatment into the interior of the vessel (3) to thereby form a vapor-deposited film on the internal surface of the vessel (3), wherein supply pipe main body (5) constructing the whole thereof consists of a material of 10*10<-6>/ DEG C or below thermal expansion coefficient, so that there is reduced the possibility of detaching of any vapor-deposited film formed on the external surface of the gas supply pipe (4) by the thermal expansion or thermal shrinkage of the gas supply pipe (4).