An image forming apparatus of the present invention includes image carriers arranged side by side in a preselected direction, developing means each for forming a toner image on one of the image carriers, a drive mechanism for driving in the preselected direction a member to which toner images are to be sequentially transferred from the image carriers one above the other, and image transferring devices each for transferring a toner image from one of the image carriers to the above member. At least during an image forming process, a slip condition is substantially the same throughout all image transfer positions where the image carriers face the member.