To make plasma distribution inside of a chamber uniform by setting a width dimension of a dielectric window provided at a part corresponding to a wave guide tune of the chamber to a multiple of the length of a half wavelength of a microwave spreading the dielectric window.

A microwave transmitted to a microwave transmission window 33 whose material is a dielectric is spread along a surface of the microwave transmission window 33 and advances toward a mounting part 34 parallel to an advancing direction of the inside of a wave guide tube 30. The microwave is reflected at the mounting part 34 to make a reflection wave, and a composite wave is formed with an incident wave and the reflection wave for that purpose. Here, the microwave transmission window 33 and the mounting part 34 are formed substantially same dimensions, however, if these dimensions are set to a multiple of the half wavelength of the microwave, the incident wave and the reflection wave interfere with each other so as to be strengthened. Therefore, the electric field intensity of the microwave is increased in the inside of the chamber 21, thereby making it possible to uniform distribution of plasmas inside the plasma generation chamber.