Abstract: A plasma treatment device for forming a high-quality thin film with fewer surface flaws and etching by preventing the generation of fine powders from deposited films in a film-forming chamber, by means of plasma treatment using gaseous starting materials. The plasma treatment chamber device includes a plasma generation chamber 11, a power-supplying mechanism for supplying power to this chamber, a film-forming chamber 113 to be spatially connected to the plasma generation chamber 11, a magnetic field generation mechanism 14 provided around this film-forming chamber for forming a multicusp magnetic field therein, an evacuation mechanism for evacuating the chamber, a first gas-supplying mechanism 16 for supplying gaseous starting materials and a second gas-supplying mechanism 17 for supplying gaseous materials for forming films. An inner wall surface 113b of the film-forming chamber is located in an area having a multicusp magnetic field with an intensity of from 50 to 200 G.