shows an example of a configuration of inspection apparatus according to embodiments of the invention hereinafter mentioned as defect inspection apparatus the defect inspection apparatus is configured to have an illumination system 100 a stage system 200 a detection system 300 a fourier transform surface observation system 500 a signal processing section 400 an observation optical system 600 and a control section 2 defect detection using the defect inspection apparatus shown in fig1 is performed according to the following procedure the illumination system 100 illuminates a wafer 1 set in the stage system 200 and the detection system 300 acquires an image of the illuminated wafer 1 the illumination system 100 adjusts output of a light source 101 by an illumination controller 103 according to an instruction value of the control section 2 as the light source 101 a laser light source is used which emits laser in an ultraviolet region having a wavelength of 400 nm or less the illumination system 100 includes a unit not shown for reducing coherency of the laser emitted from the laser light source illumination light is shaped into an appropriate form on the wafer 1 by an optical system 102 the stage system 200 includes a rotation stage 201 a z stage 202 an x stage 203 and a y stage 204 and moves with respect to the detection system 300 so that the detection system 300 can scan the whole surface of the wafer 1 the detection system 300 includes a fourier transform lens 301 spatial filter 302 focusing lens 303 and sensor 304 here the spatial filter 302 is to shield a diffraction light pattern caused by diffraction light from a repetitive pattern on the.