A plasma generation chamber of a plasma processing apparatus is closed by a top plate 3. The top plate 3 has recesses 3A on its surface facing the plasma generation chamber and a central recess 3B on an opposite surface. The top plate 3 is coupled to an antenna thereon. If a microwave is supplied to the antenna, the microwave is radiated through slots of the antenna. The microwave is propagated through the top plate 3 such that the microwave has a plane of polarization and the microwave forms a circularly polarized wave as a whole. Here, resonance absorption of the microwave occurs at a side surface of recesses 3A and the microwave is propagated within the recesses 3A in a single mode. Strong plasma can be generated within each of the recesses 3A, so that a stable plasma mode can be generated in the top plate 3.