SAMPLE INSPECTION APPARATUS, IMAGE ALIGNMENT METHOD, AND PROGRAM-RECORDED READABLE RECORDING MEDIUM

A sample inspection apparatus according to an aspect of the present invention includes a first SSD calculating unit which calculates the displacement amount from a preliminary alignment position of an optical image and a reference image to a position where the SSD of a pixel value of the optical image and a pixel value of the reference image is minimized, and a least-square method calculating unit which calculates the displacement amount by a least-square method from the preliminary alignment position of the optical image and the reference image, wherein the alignment position of the optical image and the reference image is corrected to a position where the smaller SSD of the minimum SSD obtained as the result of the calculation by the first SSD calculating unit and the SSD obtained as the result of the calculation by the determined by the least-square method calculating unit is obtained.