Abstract: Three electrodes are disposed at lateral sides of a plasma generating chamber of an etching apparatus serving as a plasma generating apparatus. A sample stage is disposed at a lower part of the plasma generating chamber, and an opposite electrode is disposed at an upper part thereof. High frequency electric power having a first frequency is supplied to the sample stage and the opposite electrode. Respectively supplied to the three electrodes 4, 5, 6 are high frequency electric powers which are oscillated by a three-phase magnetron, which have a second frequency different from the first frequency and of which respective phases are successively different by about 120.degree. from one another, thus forming a rotational electric field in the plasma generating chamber.