1. An etching method comprising the step of focusing by a projecting optical system an optical image which is reflected from a region of a dicing stripe pattern on a substrate to-be-etched during selective etching, the step of converting the focused pattern into an image signal by an image detector, the step of finding a change of contrast in the region of the dicing stripe pattern on the basis of the image signal, and the step of deciding a state of etching on the basis of the found change of contrast.