In a plasma processing method and apparatus, microwaves are radiated from a slot antenna set at the bottom of a resonator, a plasma is generated using the microwave and a sample is processed by the plasma. A plasma having a ring-form is generated by the microwaves radiated from the slot antennas, which are disposed at an angle which is neither in parallel to nor perpendicular to a surface current flowing on a slot antenna plate. Thereby, the sample is uniformly processed.