PURPOSE: To control the conditions of microwave incidence on plasma by a simple structure and provide plasma uniformity by covering the part of a plasma container with a microwave shielding wall and controlling the plasma distributing conditions in the plasma container by the position of the microwave shielding wall.

CONSTITUTION: Microwave generated by a microwave generating source 8 is transmitted to an external container 10 through a waveguide 9, is directed into a plasma container which allows electromagnetic wave permeation so as to be absorbed by plasma on an ECR plane 14 and plasma is formed. When plasma density becomes high, the quantity of reflecting microwave becomes higher than the quantity absorbed. The reflecting microwave passes through a space 15 by repeating reflection between the external container and the microwave shielding wall 12. The ratio of the incidence quantity from the plasma container top plane 7 to the incidence quantity from the plasma container side plane 7a can be varied by permitting the microwave shielding wall 12 to be vertically movable, and plasma density distribution can be controlled.