1. A wafer inspecting method comprising: multi-scanning a pattern image of a unit inspection region in a normal state and a pattern image of a unit inspection region to be inspected, respectively, with different inspection conditions; comparing the multi-scanned pattern images in the normal state with the multi-scanned pattern images to be inspected, obtained by the same inspection conditions, and storing differences of the pattern images as difference images; generating a discrimination difference image by calculating a balance between the stored difference images; and discriminating a defect from noise by using the discrimination difference image.