A method for acquiring an image, in which an image of an image acquiring region is acquired by radiating an ion beam to a sample having a conducting part with a linear edge on a dielectric substrate, includes performing an equal-width scan of the ion beam in a first direction that obliquely intersects the linear edge and sweep in a second direction intersecting the first direction. The ion beam is sequentially scanned in different patterns on different scan regions of parallelogram shape, each of which includes the image acquiring region. Secondary charged particles are detected to generate image data of all the scan regions, and image data of the scan regions are calculated to generate image data of the image acquiring region. The image data of the image acquiring region are synthesized to display the image data of the image acquiring region.
