A plasma processing apparatus is offered which has evacuable vacuum vessel, processing chamber disposed inside the vacuum vessel and having inside space in which plasma for processing sample to be processed is generated and in which the sample is placed, unit for supplying gas for plasma generation into processing chamber, vacuum evacuation unit for evacuating inside of processing chamber, helical resonator configured of helical resonance coil disposed outside the vacuum vessel and electrically grounded shield disposed outside the coil, RF power supply of variable frequency for supplying RF electric power in given range to the resonance coil, and frequency matching device capable of adjusting frequency of the RF power supply so as to minimize reflected RF power. The resonance coil has electrical length that is set to integral multiple of one wavelength at given frequency. The helical resonance coil has feeding point connected to ground potential using variable capacitive device.