Plasma processing apparatus

This plasma processing device is provided with a processing chamber in an upper part of which a dielectric plate through which microwaves pass is provided, and in which a specimen is subjected to plasma processing, a high-frequency power source for supplying high-frequency electric power for the microwaves, a cavity resonator which is disposed above the dielectric plate to cause microwaves transmitted from the high-frequency power source via a waveguide tube to resonate, and a magnetic field forming mechanism for forming a magnetic field in the processing chamber, wherein the plasma processing device is additionally provided with: a ring-shaped conductor disposed inside the cavity resonator; and a circular conductor which is disposed inside the cavity resonator and is disposed in a central opening of the ring-shaped conductor.