An image forming apparatus includes a plurality of image forming units each having a photoconductive drum for forming a latent image and a developing device for developing the latent image, for providing different-color developed images, an exposing device for projecting light according to image information, and a plurality of mirror members for controlling the optical passage of the exposing device so as to expose a selected photoconductive drum without shifting the exposing device, thereby simplifying the apparatus and allowing for a stable drive.