An image forming apparatus includes a photoconductor to form an electrostatic latent image, a special color developing device to develop the latent image with a special color toner other than standard color toners to form a special color toner image, an adhesion amount adjuster to adjust a special color toner adhesion amount by changing an application bias between the photoconductor and a developing sleeve of the special color developing device, a setting unit to set brightness of the special color toner, and a developing-performance adjuster to adjust a developing performance of the special color developing device according to a setting value of the brightness set by the setting unit. The developing-performance adjuster adjusts the developing performance of the special color developing device to a developing performance different from a developing performance set to each of standard color developing devices in adjustment of densities of the standard color toners.