The main purpose of the present invention is to suppress deposition of byproducts on an inner wall of a vacuum chamber during wafer processing using plasma generated by an inductive coupling antenna and an electrostatic capacitive coupling antenna which are connected in series at a connection point. Deposition of byproducts on the inner wall of the vacuum chamber can be suppressed by grounding the connection point of the inductive coupling antenna and the electrostatic capacitive coupling antenna via a variable-impedance load and varying an impedance of the variable-impedance load, thereby controlling a ratio of plasma produced in the chamber by electrostatic capacitive coupling discharge.