A plasma processor comprising a plasma generation portion in which a plasma is generated by electron cyclotron resonance, a source of a right hand polarized microwave and supplying it to the plasma generation portion, and a plasma reaction portion which accommodates a substrate to be processed with the plasma generated in the plasma generation portion. Owing to the production and supply of the right hand polarized microwaves, almost all of the microwaves injected into the plasma generation portion contribute to the generation of the plasma, to increase plasma density and raise processing speed.