PURPOSE: To allow judging that the applicable one belongs to one defect on the real time basis even in case part of the defect forms a neck, the density in reading is low, or the defect extends aslant.

CONSTITUTION: The image of an object to be inspected due to photographing with a line CCD camera 1 is converted into binary values by a comparator 4, and the width of an applicable defect is encoded by a run length encoder circuit 5. A CPU 15 expands the defect and classifies the condition of defect by subjecting the run length code to a coupling property processing over a plurality of continuing scanning lines, and on the basis of the defect date classified, judgement is passed whether the phenomena on the object belong to one defect.