A defect inspecting apparatus provide with an illumination optical system and a detection optical system is further provided with an image processing section, which has: a feature calculating section, which calculates a feature based on the inputted design data of the object to be inspected, and calculates a feature quantity based on a plurality of pieces of image data, which are acquired by the detection optical system and have different optical conditions or image data acquisition conditions; a defect candidate detecting section which integrates the feature obtained from the calculated design data and the feature quantity obtained from the plurality of pieces of image data and detects candidates; and a defect extracting section which extracts a highly critical defect from the detected defect candidates, based on the feature of the design data calculated by the feature calculating section.