Light beam is irradiated onto a surface of a substrate to be inspected and scattered lights from the surface of the substrate are received at different light reception angles, so that first and second light detection signals corresponding to the different light reception angles are generated. Reference function defining a correlation in level value between the first and second light detection signals is set, a comparison is made between respective level values of the first and second light detection signals using the reference function as a comparison reference, and it is determined, on the basis of a result of the comparison, which of a plurality of different types of defects, such as a foreign substance and crystal-originated pit, a possible defect present on the surface of the substrate, which is represented by the light detection signals, corresponds to. Also, the level value of a predetermined one of a plurality of the light detection signals is weighted with a predetermined coefficient, and a comparison is made between the weighted level value of the predetermined light detection signal and the level value of the remaining light detection signal, to thereby identify any of a plurality of different types of defects, such as a foreign substance and scratch, present on the surface of the substrate.