A defect-inspecting apparatus including an arrangement to convert detected light into a first signal corresponding to light illuminated by a high-angle illumination optical system and/or a second signal corresponding to light illuminated by a low-angle illumination optical system; and a classification unit which utilizes the first and second signal and classifies defects on the object to be inspected, wherein a defect size is estimated by changing a correction coefficient of the defect size on a basis of a concave-convex level (b/a), where the concave-convex level (b/a) of a defect is indicated by a ratio of a size b of a first direction of the defect to a size a of a second direction of the defect, where the second direction is lateral to the first direction.