The present invention provides a plasma processing unit comprising: a processing vessel having an opening on a ceiling side thereof, and capable of creating a vacuum therein; a stage disposed in the processing vessel, for placing thereon an object to be processed; a top plate made of a dielectric, the top plate being hermetically fitted in the opening and allowing a microwave to pass therethrough; a planar antenna member disposed on the top plate, the planar antenna member being provided with a plurality of microwave radiating holes for radiating a microwave for plasma generation toward an inside of the processing vessel; a slow-wave member disposed on the planar antenna member, for shortening a wavelength of a microwave; and a microwave interference restraining part disposed on a lower surface of the top plate, the microwave interference restraining part separating the lower surface into a plurality of concentric zones and restraining a microwave interference between the zones.