Abstract: An original document for facsmile transmission or the like is fed over a horizontal transparent platen by rollers for scanning. A light source illuminates the document and a mirror reflects a light image of a linear portion of the document perpendicular to the direction of movement horizontally to a converging lens. The light image from the lens is reflected upwardly by another mirror onto the light receiving surface of a linear photosensor array. The light receiving surface of the array faces downwardly, minimizing accumulation of dust thereon. A light baffle in the form of a box is provided between the first mirror and converging lens and is formed with apertures for the light image to pass therethrough. A scan drive and amplifier circuit for the array is mounted closely adjacent thereto while a signal processing circuit comprising a quantization means is mounted on the box and electrically connected to the drive unit. The various units of the apparatus are individually detachable for ease of servicing.