The invention relates to a defect inspection apparatus in which images of mutually corresponding areas in identically formed patterns on a sample are compared to detect mismatched portions of the images as defects. The defect inspection apparatus includes an image comparator that creates a feature space with the use of feature quantities calculated from pixels of images acquired under different optical conditions and detects outlier values in the feature space as defects. Thus, the defect inspection apparatus can detect various defects with high sensitivity even if there are luminance differences between images of identical patterns which are attributable to the difference in wafer pattern thickness.