According to one embodiment, an image forming apparatus of the embodiment includes a roller, a plurality of developing units, an image forming unit, a sensor, and a control unit. The rollers carry a sheet. The plurality of developing units include different types of developing materials. The image forming unit forms a plurality of images on a transfer belt by the developing materials of each of the plurality of developing units. The sensor reads the plurality of images formed on the transfer belt. The control unit controls the speed of the roller based on the positions of the plurality of images read by the sensor.