PURPOSE: To make controllability at the time of maximum output setting ever so better, by constituting an accelerating power source for an ion implanter or the like to feed a difference between output voltage of a high-tension side power source and that of a grounding side power source back to a high-tension side power source differential amplifier.

CONSTITUTION: An accelerating power source available for an ion implanter or the like is formed with a high-tension side power source 4 and a grounded side power source 5, and those of output voltage are connected together in series whereby a high voltage is made so as to be generated. At this time, the output voltage of the grounded side power source 5 is fed back to a differential amplifier 13, compared with an HV2 setter and thereby controlled. And, the output voltage of the high-tension side power source 4 takes a difference with the output voltage of the grounded side power source 5 at a differential amplifier 14 and fed nack to it, and controlled in comparison with an HV1 setter at a differential amplifier 9. Therefore, first HV1 is set in advance, then HV2 is set whereby the maximum output voltage can be set so as to be bottomed up, thus controllability is improvable as two operations.