An image forming apparatus includes an image forming unit that forms multicolor toner images superposed on a transfer belt. A sensor is disposed in an image formation region and detects a pattern on the transfer belt. A controller determines, when image data is received, whether or not a region of a toner image based on the image data will be superposed on a region of the pattern. The controller controls the image forming unit to form the toner image based on the image data and the pattern simultaneously on the transfer belt when the controller determines that the region of the toner image based on the image data will not be superposed on the region of the pattern.