JPS5845068B

PURPOSE:To attain accurate detection by making even an influence of a black line by forming marks, differing in reflection coefficient, in stripes and by detecting magnification from the states of their read output. CONSTITUTION:OCR gauge 6 is provided with striped mark 6 formed of sections M1-M65, which are irradiated with light from lamp 11 and their images are formed on line sensor 5 through lens 12. Then, sensor 5 is driven by sensor driving circuit 14 to take a scan and the image is observed through synchroscope 16 being amplified by amplifier 15. Since photoelectric elements of sensor 5 correspond to respective sections of mark 6, odd-numbered and even-numbered photoelectric elements are nearly equal in output and have no node as far as the magnification is precise and when not, nodes are seen. When the magnification is further precise, an output where the lens is in the best focus increases, the point in the best focus can be observed.