1. A method of obtaining a confocal STEM image, comprising the steps of: scanning an electron beam over a sample in two dimensions; detecting a diffraction image signal emanating from the sample by a detector; converting the diffraction image signal detected by the detector into digital data; storing the digital data as image data into a memory; extracting diffraction images respectively corresponding to successive pixel positions from images stored in the memory; selecting center positions of the extracted diffraction images corresponding to the pixel positions and correcting the center positions; creating an image set having diffraction information in which the center positions of the diffraction images respectively corresponding to the pixel positions have been corrected and aligned; selecting only innermost portions of the diffraction images of the created image set which correspond to the successive pixel positions; and reproducing STEM images from the diffraction images, thus obtaining a confocal STEM image.