An image forming apparatus includes first and second drums subjected to image formation by exposure to light at exposure positions to form latent images and then transferring toner images, formed by developing the latent images with toner, onto a transfer material at transfer positions; first and second gears provided coaxially and integrally with the drums; a driving source for rotationally driving the drums; and a branch gear, meshable with the first and second gears at first and second mesh points, for transmitting a driving force from the driving source to the first and second gears. A sum of a time of movement of a portion of the branch gear located at the first mesh point to the second mesh point and a time of integer-time rotation of the branch gear is equal to a time of movement of the transfer material from the transfer position of the first drum to that of the second drum.