PURPOSE: To read an image at a high speed without decreasing the quantity of light nor causing any position shift by guiding reflected light from an original surface to a photodetection sensor through plural lenses which are arranged successively and a color separation filter which is provided corresponding to the each lens, and projecting and forming an image of the overall slit length of an original surface.

CONSTITUTION: The lenses 61, 62, and 63 are arrayed on the same plane in the optical paths from the mirrors 3, 4, and 5 in the lengthwise direction of the slit, the separation filters 71, 72, and 73 which differ in color from one another are arranged behind the lenses, and the photodetection sensors 81, 82, and 83 such as CCD are provided on image-formation positions in the optical paths from the filters. In this constitution, slit light of the overall width W of the original O is incident to the respective lenses 61, 62, and 63 and separated by the color separation filters 71, 72, and 73 into light components differing in color, and the sensors 81, 82, and 83 obtain respective pieces of color information on the overall width W of the original.