PURPOSE: To simplify the circuit constitution as well as to increase the accuracy by using the matching pattern of both the thin and thick patterns as the reference pattern for decision of the quality.

CONSTITUTION: The thin pattern (a) and thick pattern (b) are memorized previously in the computer, and mark X and its periphery Y are scanned via the TV camera system. Then the video signals are fed into the computer to secure the matching between patterns (a) and (b). First, the matching is secured between pattern (a) and mark X to be decided to identify the gradation of mark X caused by the brightness levels at the area of mark X as well as the mark break. While the matching is obtained between pattern (b) and mark X to identify the excessive thinness or thickness of the line, the blur and the ink splash at the periphery of mark X. Thus, nondefective patterns (a) and (b) are decided as good products finally.