An image forming apparatus includes an image carrier, a rotary developer unit having a developing roll opposed to the image carrier when located at a developing position and an exposure device for writing a latent image onto the image carrier, wherein an optical path from the exposure device to the image carrier passes within a circumscribed circle of the developing roll with the center of rotation of the rotary developer unit as the center of the circle. The image carrier is located so as to provide the developing position above a horizontal line passing the center of rotation of the rotary developer unit, and the exposure device is located so as to provide a beam exit position below the horizontal line.