An image forming apparatus that includes an imaging device, a transferrer, a rotator, a rotation position sensor, an adhesion amount sensor, a power supply, and a controller. The controller executes a construction process to construct output pattern data to change a voltage output from the power supply, according to a result obtained by detecting a toner adhesion amount of a toner image for density unevenness detection and a detection result from the rotation position sensor obtained when the toner image is formed, and an output change process to execute a predetermined process while changing the voltage according to the detection result and the output pattern data. The controller executes a determination process to determine propriety of an output range of the voltage output from the power supply by the output change process and a data process for a shift to shift the range when a determination result is inappropriate.