A pattern inspection apparatus includes a pulse laser light source sequentially generating pulse laser light, an illumination optics applying the pulse laser light onto a mask substrate, an imaging optics collecting light from the mask substrate to form an image thereof, an area sensor sensing the image of the mask substrate obtained by the optics in a rectangular area unit, a comparator comparing image data acquired by the area sensor with previously prepared reference data to detect a defect of a pattern, a stage driving apparatus two-dimensionally scanning a stage having the mask substrate placed thereon, and a stage position detector detecting a position of the stage. With the above configuration, it is possible to efficiently inspect the surface of the mask substrate by adequately setting the moving speed of the mask substrate and the sensing timing of the sensing apparatus.