An image forming apparatus is provided. The image forming apparatus includes an image forming device to form images of color toners on corresponding image bearers of at least four image bearers; a transferring device to transfer the color toner images on the image bearers to a transfer medium; and a controller to control the image forming apparatus. The controller performs a compulsory toner consumption processing for the color toners to compulsory consume deteriorated toners. When the compulsory toner consumption processing is performed on three or more toners, compulsory consumption toner images of the color toners are formed on the corresponding image bearers and then transferred to the transfer medium to form a compulsory consumption combined toner image including at least two overlaid image portions, wherein the at least two overlaid image portions are arranged side by side with a space therebetween in a width direction of the transfer medium.