An image forming apparatus includes an image bearer, an intermediate transferor, a secondary transferor, a plurality of rotators including a secondary driving rotator, and a detector. The image bearer bears a detection image. The detection image is transferred from the image bearer to the intermediate transferor at a primary transfer position. The secondary transferor is looped around the plurality of rotators and disposed in contact with the intermediate transferor at a secondary transfer position where the detection image is transferred from the intermediate transferor to the secondary transferor. The secondary driving rotator drives the secondary transferor. The detector detects the detection image on the secondary transferor at a detection position. With this configuration, a distance from the secondary transfer position to the detection position on the secondary transferor is an integral multiple of a circumference of the secondary driving rotator.