PURPOSE: To stabilize reading precision by providing a compensation means always invariably retainging an optical path length between the surface position of a paper where reading information is described and a photoelectric conversion element.

CONSTITUTION: Since CCD 14 is fixed to a housing 13 at its both ends, when a paper 18 is pinched between a transfer roller 16 and a roller 11 and the roller 11 is moved upward, the CCD 14 is moved along with the housing 13 by the amount of the movement. That is, when the roller 11 is moved up by the amount equivalent to the thickness of the paper 18, the CCD 14 is also moved up by the same amount. Accordingly, the optical path between the surface of the form 18 and that of the CCD 14 is kept constant. Under such condition, while the paper 18 is transferred in a direction (a), the optical image of characters described and graphics drawn on the surface of the form 18 are picked up on the surface of the CCD 14 via the transparent roller 11 and an image signal corresponding to the optical image is outputted to an image processing circuit, etc., from the CCD 14.