PURPOSE: To make the device small and to improve the performance by providing a rotating body of a stripe pattern not in parallel with a rotary shaft and reading an original through the pattern detection by plural light receiving elements so as to simplify the optical system and to facilitate the focus adjustment.

CONSTITUTION: A rotating body 1 is arranged in the vicinity of a read window frame 4 with which an original is abutted on such as a target glass and a stripe pattern not in parallel with the rotary shaft is provided to the surface of the rotating body. Then the movement of the pattern is read by a section of an image sensor other than an original read section and the motion in the subscanning direction with respect to the original is sensed based on the result of reading thereby deciding a read timing of the original. Since a picture signal resulting from reading the original is selected by the combination of the detection operations of plural light receiving elements in this way, a rough resolution is enough and it is possible to provide a rough pattern density and a thick pattern width required for the purpose. Thus, the focus is adjusted roughly and a required output to an encoder section is obtained.