The invention provides a plasma processing apparatus capable of minimizing the non-uniformity of potential distribution around wafer circumference, and providing a uniform process across the wafer surface. The apparatus is equipped with a focus ring formed of a dielectric, a conductor or a semiconductor and having RF applied thereto, the design of which is optimized for processing based on a design technique clarifying physical conditions for flattening a sheath-plasma interface above a wafer and the sheath-plasma interface above the focus ring. A surface voltage of the focus ring is determined to be not less than a minimum voltage for preventing reaction products caused by wafer processing from depositing thereon. The surface height, surface voltage, material and structure of the focus ring are optimized so that the height of an ion sheath formed on the focus ring surface is either equal or has a height difference within an appropriate tolerance range to the height of the ion sheath formed on the wafer surface. Optimization of the structure is realized by setting up an appropriate tolerance range taking into consideration the variation caused by consumption of the focus ring.