A plasma processing apparatus includes a processing vessel, a means for holding a substrate to be processed, an evacuation system coupled to the processing vessel, a means for supplying plasma gas to an interior of the processing vessel, a microwave antenna provided on the processing vessel, and a process gas supply part comprised of two components. The first component includes a plurality of first apertures for passing through plasma formed in interior of the processing vessel, a process gas passage, and a plurality of second apertures in communication with the process gas passage. The second component includes a plurality of third apertures axially aligned with the first apertures in the first component and diffusion surfaces upon recessed areas of the second component, located opposite to the second apertures in the first component.