Abstract: The present invention relates to a microwave plasma processing apparatus for processing such as thin film formation, etching, sputtering, and plasma oxidation, etc., on a surface of a processing object by utilizing a high density plasma generated by electron cyclotron resonance. A vacuum vessel of the apparatus, in which a microwave transmitted by a microwave guide is utilized for converting gas supplied to the vacuum vessel to plasma for the plasma processing of the processing object placed in the vacuum vessel, is formed in, such manner that the interior space of the vacuum vessel extends beyond the outer periphery of magnetic field generating coils, and the extended portion of the vessel is provided with a gas outlet for connection with an evacuation apparatus to evacuate the interior of the vacuum vessel to a desired vacuum degree.