This invention provides a technique which allows more faithful color reproduction by a relative simple arrangement. To this end, according to this invention, by time-divisionally driving R, G, B, and E LEDs respectively having dominant emission wavelengths of 630 nm, 525 nm, 470 nm, and 500 nm, a common monochrome line image sensor (102) scans a document image. Scanned image data of respective color components undergo correction equivalent to that attained by shifting the barycentric positions of respective wavelength distributions so as to become closer to the CIE-RGB sensitivity distributions.