In an image forming apparatus, when some of a plurality of image supporters which are preceded by another image supporter on an upstream side of the carrying direction are referred to as downstream side image supporters, a control section derives a toner supply amount for each of positions in a main-scanning direction for each of downstream side image supporters based on image data for the downstream side image supporters and image data for an upstream side image supporter, and thereafter generates patch image data that represents the derived toner supply amount, and the exposure section further scans each of the downstream side image supporters in the main-scanning direction with an optical beam modulated according to the patch image data generated by the control section.