A CMOS sensor scans an image that is either on a transfer material carrier or on a transfer material that is placed on the transfer material carrier. A sampling timing controller samples an image signal at a predetermined sampling rate and computes a position of a predetermined pattern contained within the sampled image signal. A speed computation processor computes a moving speed of either the transfer material carrier or the transfer material, based on the position of the predetermined pattern thus sampled at the predetermined sampling rate and computed, as well as the predetermined sampling rate. The image region that the CMOS sensor scans is determined in accordance with the rotational speed of the drive motor and the sampling rate.