An object of the invention is to provide a method and an apparatus for plasma processing which can accurately monitor an ion current applied to the surface of a sample. Predetermined gas is exhausted via an exhaust port 11 by a turbo-molecular pump 3 while introducing the gas within the vacuum chamber 1 from a gas supply device 2, and the pressure within the vacuum chamber 1 is kept at a predetermined value by a pressure regulating valve 4. A high-frequency power supply 5 for a plasma source supplies a high-frequency power to a coil 8 provided near a dielectric window 7 to generate inductively coupled plasma within the vacuum chamber 1. A high-frequency power supply 10 for the sample electrode for supplying the high-frequency power to the sample electrode 6 is provided. A matching circuit 13 for the sample electrode and a high-frequency sensor 14 are provided between the sample electrode high-frequency power supply and the sample electrode 6. An ion current applied to the surface of a sample can be accurately monitored buy using the high-frequency sensor 14 and an arithmetic device 15.