There is provided a focused ion beam processing method in which damage to a workpiece is minimized when the surface of the workpiece is irradiated and processed with an ion beam. The method comprises the steps of: generating an acceleration voltage between an ion source and a workpiece; focusing an ion beam emitted from the ion source; and applying the ion beam to a predetermined process position to process the surface of the workpiece. In this process, the energy level of the ion beam produced by the acceleration voltage is set within a range from at least 1 keV to less than 20 keV.