Abstract: In a plasma processing apparatus, a second microwave guiding unit has at least one vacuum waveguide with a dielectric window and an opening being formed on the side of the microwave introducing hole. The vacuum waveguide is arranged at a position where an external magnetic field applied from an external magnetic field applying unit is stronger than an ECR condition, and causes the microwave guided from a first microwave guiding unit to propagate through the dielectric window in a direction perpendicular to the external magnetic field such that the electric field of the microwave is parallel to the external magnetic field applied to the second microwave guiding unit by the external magnetic field applying unit. The dielectric window is arranged at a position at which at least a portion of the dielectric window cannot been seen directly from the microwave introducing hole.