PURPOSE: To compensate for mechanical displacement in the stage of manufacturing charged particle source and stably generate ion beam by disposing the leadout electrodes on the same surface after splitting the electrode into three leadout electrode leaves and simultaneously controlling differences of voltages applied to respective electrode leaves.

CONSTITUTION: A leadout electrode 10 is splitted into the electrodes 10aW10d. The potensiometers 11, 12 and 13 are respectively operated in conjunction and supply divided voltages to the electrodes 10aW10d. A voltage is applied across the emitter 1 and acceleration electrode 3 from the acceleration voltage source E2, and moreover a leadout voltage is applied across the emitter 1 and the electrode 10 from the power source 7. An ion beam current flowing into the aperture 4 is controlled to a constant value by a negative feedback circuit consisting of the conversion circuit 5, setting circuit 6 and power source 7. A mechanical displacement generated during manufacture of emitter 1, electrode 10 and electrode 3 can be electrically compensated by adjusting the potensiometers 11W 14 and thereby a stable charged particle source can be obtained.