PURPOSE: To unfailingly find out defects including cracks on the surface of an object, for example, a semiconductor substrate, by successively radiating to a surface of a semiconductor substrate rays of light from a plurality of light sources disposed in different positions around the semiconductor substrate.

CONSTITUTION: Light sources 13, 23, 33, 43 disposed around a semiconductor substrate 2, which is placed on an object stage 1a of a stereoscopic microscope 1, are turned on and off in order. When there is a crack 4 on the surface of the substrate 2, the direction in which an inclined portion 4a of the crack 4 is extended is different from at least one direction among a plurality of directions in which rays of light are radiated from the light sources 13, 23, 33, 43, so that the crack 4 castes a shadow 5. Therefore, the crack 4 can be found out unfailingly.