| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical system unit (ISU) for reading images that can secure constant CCD output even if the quantity of light in a light source decreases, and can always form stable images. SOLUTION: In the image-reading optical system unit, at least a light source and a CCD element 36 are provided on the lower surface of contact glass 22a and 22b, and manuscript reflection light on the contact glass from the light source 30 is received by the CCD element for reading information on the manuscript images. In the image-reading optical system unit, a reference reflection sheet is provided at a position that is illuminated with light from the light source and is outside the region of the maximum manuscript width and at a position for receiving the reflection light by the CCD element, thus increasing the amplification rate of the CCD element when the CCD output when the reflection light from the reference reflection sheet is received by the CCD element decreases by a fixed value or less.
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