A toner supply control system for an image forming apparatus includes a supply controller to compute a toner supply amount required for a toner supply operation to cancel a toner concentration fluctuation in the developing agent. The supply controller includes an image-information-based consumption prediction unit to predict toner consumption amount based on image information used for forming an image; a toner-concentration-based consumption prediction unit to predict toner consumption amount based on a detection result of a toner concentration detector; and a toner supply determination unit to determine a toner supply timing and amount and initiate a toner supply operation based on the toner consumption amount predicted by the toner-concentration-based consumption prediction unit right after the toner consumption occurs. When the toner-consumed developing agent comes to a toner supply area again after the toner consumption occurs, a toner supply operation is initiated using a toner amount computed based on the image information in view of the already supplied toner.