An ion implanter includes a high-voltage power supply, a control unit that generates a command signal controlling an output voltage of the high-voltage power supply, an electrode unit to which the output voltage is applied, and a measurement unit that measures an actual voltage applied to the electrode unit. The control unit includes a first generation section that generates a first command signal for allowing the high-voltage power supply to output a target voltage, a second generation section that generates a second command signal for complementing the first command signal so that the actual voltage measured by the measurement unit becomes or close to the target voltage, and a command section that brings to the high-voltage power supply a synthetics command signal which is produced by synthesizing the first command signal and the second command signal.