A microwave plasma processing apparatus including a processing space; a dielectric window having a facing surface facing the processing space; and an antenna plate installed on a surface of the dielectric window opposite to the facing surface, and formed with a plurality of slots configured to radiate microwaves for plasma excitation to the processing space through the dielectric window. The plurality of slots includes a first slot group configured to transmit microwaves guided to a center side of the dielectric window, and a second slot group configured to transmit microwaves guided to a peripheral edge side of the dielectric window. The dielectric window includes a first concave portion in a region corresponding to the first slot group of the antenna plate on the facing surface, and a second concave portion in a region corresponding to the second slot group of the antenna plate on the facing surface.