A plasma processing apparatus for generating highly-uniform and stable plasma. In an apparatus for generating plasma by using a μ wave, concerning a method for rotating the μ wave in terms of time, a plurality of (larger than two and smaller than four) waveguides are used, then forming an angle between the respective waveguides, and setting a phase difference between respective electric fields therein. This configuration allows introduction of the circularly polarized wave into a processing chamber. At this time, there are provided configuration components such as a waveguide locating method, a unit therefor, a μ-wave merging box, and a reflective-wave control unit using a reflection control chamber.