A defect inspection apparatus is capable of inspecting an extremely small defect present on the top and edge surfaces of a sample such as a semiconductor substrate or a thin film substrate with high sensitivity and at high speed. The defect inspection apparatus has an illumination optical system, a plurality of detection optical units and a signal processor. One or more of the detection optical units receives either light diffracted from an edge portion of the sample or light diffracted from an edge grip holding the sample. The one or more of the detection optical units shields the diffracted light received by the detection optical unit based on a signal obtained by monitoring an intensity of the diffracted light received by the detection optical unit in order to inspect a sample portion located near the edge portion and a sample portion located near the edge grip.