PURPOSE: To perform a continuous plasma processing of a thermoplastic resin with a high productivity in a energy-saving manner by a method wherein a thermoplastic resin is introduced into vacuum plasma generation area for a low-temperature plasma processing via an area with the pressure boosted incrementally.

CONSTITUTION: A thermoplastic resin charged into an extrusion molding machine 3 is molded by direct extrusion from an extrusion die 4 and introduced into a vacuum plasma processing chamber 1 as vacuum plasma generation area. A gas such as air, oxygen and nitrogen is introduced into the vacuum plasma processing chamber 1 from a gas introduction port 8 while the vacuum plasma processing chamber 1 is made vacuum by exhaustion through an exhaust chamber 9. Then, a thermoplastic resin sheet or film is introduced between electrodes 7 and 7' for a low-temperature plasma processing. The sheet or film thus subjected to the low-temperature plasma processing is cooled with a cooling roll 10 and then, introduced into a prevacuum chamber 6. Then, it is boosted in the pressure in the prevacuum chamber 1 incrementally and while approaching the atmospheric pressure, it is drawn out of the chamber 1 to be taken up with a take-up unit 11.