Image forming apparatus that suppresses occurrence of color shift in images and method of controlling the same

An image forming apparatus (1000) that suppresses occurrence of color shift in images transferred from image bearing members (100Y, 100M, 100C, 100K) onto an intermediate transfer member (108). A surface of each of a first photosensitive drum (100Y) and second photosensitive drums (100M, 100C, 100K) is charged. An exposure device (101Y, 101M, 101C, 101K), provided for each photosensitive drum, forms an electrostatic latent image by exposing an associated one of the charged photosensitive drums. A developing device, provided for each photosensitive drum, develops the electrostatic latent image with toner. An intermediate transfer belt friction-drives the photosensitive drums for rotation and has the developed images transferred thereon. Timing for exposing the second photosensitive drums is controlled based on a first surface distance (Ly) from an exposure light irradiated position to a primary transfer position of the first photosensitive drum, and a second surface distance (Dym, Dyc, Dyk) from an exposure light irradiated position of each second photosensitive drum to a primary transfer position thereof.