PURPOSE: To limit the number of captured charged impurities near a processed object and to improve irregularities in process by providing an electrode assembly which supplies plasma with electric potential, and providing the electric assembly with a means for controlling the plasma irregularities. CONSTITUTION: An electrode assembly which supplies plasma with electric potential is provided, and the electrode assembly is provided with a means for controlling the plasma irregularities. For example, a buried element 60 is inserted in the electrode assembly which uses an electrode static chuck 38 as a means for fixing a processed object. The buried element 60 is generally annular in shape and allocated near an end part 54, under the periphery end part 54 of the processed object. As a material for the buried element 60, any which can charge an electrostatic capacity of the electrode assembly is used, for example, a couple of the buried element 60 of Teflon (registered trademark) and an electrode assembly of quartz. COPYRIGHT: (C)1995,JPO