An apparatus and method for detecting defects on a specimen includes an illumination optical unit which obliquely projects a laser onto a region which is longer in one direction on a surface of a specimen than in a transverse direction, a table unit which mounts the specimen and which is movable, a detection optical unit which detects light from the specimen illuminated by the laser with an image sensor while the table is moving, and a signal processor. The signal processor processes a signal outputted from the image sensor of the detection optical unit and converted to a digital signal and extracts defects of the specimen by comparing the converted digital signal with a reference digital signal. A display unit displays information of defects extracted by the signal processor.