METHOD FOR DIAGNOSING OPTICAL DEVICES INSTALLED IN IMAGE READING APPARATUS AND IMAGE FORMING APPARATUS

In a method for diagnosing an optical device, the positions of intersections between a scanning line and the line segments of an adjustment mark provided in a predetermined position, and output levels at the intersections are detected on the basis of the output characteristic of an output level corresponding to each pixel position and obtained by reading the adjustment mark along the scanning line. The detected output levels are compared with a predetermined value to detect an error due to the attachment position of the optical device.