An antenna electrode having a substantially circular shape, is arranged on a plane of a processing vessel, which is located opposite to a stage for mounting a sample within the processing vessel, and positioned parallel to the stage. An emission monitor monitors emission intensity of plasma present in at least 3 different points along a radial direction of the antenna electrode. A control unit adjusts an energizing current supplied to an external coil for forming a magnetic field within the processing vessel. The control unit adjusts the energizing current supplied to the external coil based upon the monitoring result obtained from the emission monitor so as to control the emission intensity of the plasma to become uniform emission intensity.