PURPOSE: To simply clean plural electrodes for extracting ion beams without detaching an ion source by moving the electrodes having many small holes in a plane perpendicular to the direction in which the ion beams are extracted with an electrode moving device.

CONSTITUTION: Gas G is introduced into an arc chamber 2 provided with a magnet 8 for confining plasma from the gas introducing hole 4, plasma is generated with a filament 6 and ion beams 20 are extracted from the plasma with an extracting electrode system consisting of an acceleration electrode 12, a deceleration electrode 13 and an earthing electrode 14 each having many small holes all over. An electrode moving device 24 or 26 is fitted to at least one electrode in the electrode system 10 so that the electrode can be moved in the directions of arrows A or B in a plane perpendicular to the direction in which the ion beams 20 are extracted. Thus, deposits on the electrodes 12W14 are sputtered with ion beams 20 to clean the electrodes.