For an automatic defect inspection of an edge exposure area of a wafer, an optical unit supplies a light beam onto the edge portion of a wafer and a detection unit detects light reflected from the edge portion. The detection unit converts the detected light into an electrical signal to transmit the electrical signal to a processing unit. The processing unit analyzes the electrical signal to measure the reflectivity of the edge portion, compares the measured reflectivity with a reference reflectivity, and calculates the width of the edge exposure area. The processing unit compares the calculated width with a reference width to detect any defect in the edge exposure area.