PURPOSE: To make it possible to control only a direct-current bias without depending on a high-frequency power, by changing the area of an earth electrode exposed to a plasma, by moving the earth electrode.

CONSTITUTION: A microwave generating device 8, a waveguide 9 guiding a microwave, a magnetic field generating device 10 impressing a magnetic field, a reaction chamber 1, a gas introducing means 7 of introducing a gas to be made into a plasma, and a stage electrode 3 whereon a semiconductor substrate 2 is set, are provided. Besides, an earth electrode 12 which can be so moved as to change the area of exposure to the plasma in the reaction chamber 1, a driving means 14 of driving the earth electrode 12 and a high-frequency power source 4 connected to the stage electrode 3 are equipped. According to this constitution, it is possible to control only a direct-current bias and thereby to control the shape of etching, a damage to the ground of a film to be etched, etc., without changing the state of the plasma.