PURPOSE: To provide a detecting method for detecting defects of a glass edge such as 'chippings', 'points' or the like generated after the glass for automobiles, etc., is cut and polished in a manufacturing line, with applying an image processing technique.

CONSTITUTION: The image data in the vicinity of the polishing face 3 of an edge of a glass 2 is input and stored in an image processor 4 by a CCD camera 1. The image data is converted to a binary image (512×512 pixels) 5 expressed only by white and black. Then, pixels in each line are retrieved from above the line (in a direction of an arrow X) and below the line (in a direction of an arrow Y). Coordinates values of a point (pixel) A and a point B where black is changed to white for the first time are obtained. The difference Di= Ci-Ci-1 of a difference Ci-1 of a next line from a difference Ci=Bi-Ai wherein Ai is a coordinate value of the point A and Bi is a coordinate value of the point B is obtained. If Ci=0 or Di>L (judging value), it is determined that the inspecting glass 2 is defective.