Abstract: A plasma processing apparatus according to the present invention includes a microwave guide for introducing a microwave, an air-tight chamber for internally setting an object to be processed, for generating a plasma by introducing the microwave introduced by the microwave guide and by supplying a reaction gas, and for processing the object by an active species generated by the plasma, a dielectric window provided between the microwave guide and the air-tight chamber, for enclosing the air-tight chamber, a top plate provided with a microwave guide port arranged with a gap maintained from the dielectric window, and cooling means provided for the top plate, for cooling heat caused by generation of the plasma, e.g., a cooling means for causing a cooling gas to flow in the gap between the dielectric window and the top plate.