An image forming apparatus includes an image bearing member having a photosensitive layer; toner image forming means for forming a detection toner image not to be formed on a recording material on the image bearing member; detecting means for optically detecting the detection toner image; control means for controlling a toner image forming condition of the toner image forming means on the basis of a result of detection of the detecting means; a transfer member for electrostatically transferring a toner image from the image bearing member onto a transfer material at a transfer region; constant voltage control means for providing a constant voltage applied to the transfer member; and voltage applying means for applying to the transfer member, when the detection toner image passes the transfer region, a predetermined voltage, controlled by the voltage control means, which has the same polarity as a charge polarity of toner.