PURPOSE: To detect a flaw at high speed by shielding the regularly reflected light in an entire scanning line region and allowing only scattered light to pass by providing a slit disc in place of a light shielding body when the flaw of a planar plate such as an fine object having a mirror surface, for example, a solar cell is inspected and rotationally driving the disc in synchronous relation to a scanning line.

CONSTITUTION: The laser beam 20 from a laser oscillator 1 is passed through a collimator lens 2 to be brought to parallel beam which is, in turn, condensed to a surface to be inspected by a lens 3. At this time, the beam is defected by a galvanomirror 4 to scan the surface to be inspected and the reflected and scattering beams generated from the surface to be inspected are allowed to be incident to a slit disc 5. At this time, the distance between the lens 3 and the surface to be inspected is set to l1 and the disc 5 is set to l2 to set the relation between both distances to l1=2l2. By this constitution, the beam diameter on the disc 5 becomes extremely fine and scattered beam passes through the slit disc 5 to be incident on a photoelectric sensor 7 through a glass fiber bundle 6.