A plasma processing apparatus includes a processing container 53, a mounting table 61 for supporting a semiconductor wafer W arranged in the processing container 53, an endless-and-annular antenna 73 attached to a sealing plate 55 opposing the wafer W to introduce a microwave into the container 53 through the plate 55, a propagation waveguide 81 connected to the annular antenna 73 to supply the microwave to the antenna 73, and a microwave supplier 83 connected to the propagation waveguide 81 to supply the microwave to the waveguide 81. In arrangement, the annular antenna 73 is arranged so that its part along the sealing plate 55 accords with an antinode of a standing wave of the microwave, producing an uniform plasma in the processing container 53.