Since a diffraction phenomenon occurs in the electron beam passing through a differential evacuation hole, an electron beam whose probe diameter is narrowed cannot pass through a hole having an aspect ratio of a predetermined value or more, and accordingly, a degree in vacuum on the electron beam side cannot be improved. By providing a differential evacuation hole with a high aspect ratio in an ion beam device, it becomes possible to obtain an observed image on a sample surface, with the sample being placed under the atmospheric pressure or a pressure similar thereto, in a state where the degree of vacuum on the ion beam side is stabilized. Moreover, by processing the differential evacuation hole by using an ion beam each time it is applied, both a normal image observation with high resolution and an image observation under atmospheric pressure or a pressure similar thereto can be carried out.