An image forming apparatus includes a plurality of image forming units having photoconductive devices for forming a latent image and developing devices for developing the latent image, an exposing device for selectively moving to and exposing the respective photoconductive devices, an endless transfer belt for conveying a sheet of paper with respect to the photoconductive devices, and transfer chargers. The apparatus is compact because only the light and small exposing device shifts, thereby enhancing picture quality and performing high-speed printing in stable driving.