To quickly and accurately recognize foreign matters such as dust and a stain attached to platen glass 32 and an original size.

In this original reader, a reflecting surface of a lighting background body composed of a conveyance roller 33c, or the like arranged so as to cover at least a portion of the platen glass 32 on which an original is mounted from the above is colored by any of three primary colors of pigments (paint), and a displacement area identifying means is provided, which detects foreign matters or an original edge on the platen glass 32 on the basis of color separation data about complementary colors in color separation data read by a color reading means 31.