Disclosed is a plasma processing apparatus that includes a processing container configured to accommodate a wafer, and a dielectric window provided to hermetically seal an opening formed in a top portion of the processing container, and configured to transmit microwaves into the processing container. The dielectric window has a thickness of 3λ/8 or less (here, λ is a wavelength of the microwaves) at least at a predetermined position where a microwave power is concentrated, and a protrusion is formed at the predetermined position on a bottom surface of the dielectric window to protrude downward from the bottom surface.