PURPOSE: To detect only flaw regardless of fluctuation of surface roughness or reflectance of an object to be inspected.
CONSTITUTION: Preliminary scanning is performed by one or more line prior to scanning on the entire surface of an object to be inspected and variation of the amount of light detected through a photoelectric converting element 7 is subjected to A/D conversion through an A/D converter 8 and the data is stored. An operational processing unit 9 determines average value and standard deviation of the amount of reflected light based on the data thus stored. Threshold level of a flaw detecting circuit 10 is set at a level deviated by a predetermined multiple of the standard deviation from the average amount of reflected light determined through the operational processing unit 9 and the flaw detecting circuit 10 makes a decision of flaw when the data traverses the threshold level.
SAKAKI TAIZO
MORITA NOBUHIRO
