PURPOSE: To easily evaluate and adjust an optical system unit in a short time before the unit is incorporated in a device by arranging testing jigs carrying test patterns in the reading the scanning area of the unit and picking up and displaying the images of the patterns.

CONSTITUTION: An optical system unit 20 is positioned on the unit placing stage of the device for evaluating and adjusting optical system unit by means of positioning pieces and testing jigs 70 are arranged in the reading and scanning area of the unit 20. Then, the optical image information of test patterns 80 (A-C and D-F) are picked up with an image pickup means 71 composed of a CCD sensor, etc., and the information is displayed by controlling the lighting and driving of a light source lamp 23 and reading of mirrors 25, 27, etc. The focusing, magnification, lateral deviation, positional deviation of front end, and distortion of the unit 20 are evaluated from the displayed patterns 80 and, when adjustment is required, the inclination, position, etc., of each of each mirror 25, 27, 29, 31, and 33 and a lens unit 35 for forming image of reflected light are adjusted.