In a plasma processing method, on a back side of a cathode electrode is provided at least one conductor plate d.c. potentially insulated from the cathode electrode and an opposing electrode, and the cathode electrode and the conductor plate are enclosed with a shielding wall such that a ratio of an inter-electrode coupling capacitance provided by the cathode electrode and the opposing electrode to a coupling capacitance provided by the cathode electrode and a bottom surface of the shielding wall on the back side of the conductor plate is not less than a predetermined value. Thereby, a high-quality, high-speed plasma processing is realized.