Electron generating devices and LED arrays are arranged in a surrounding area of a photosensitive drum. The electron generating devices are located downstream of a cleaner and upstream of a developing unit with respect to a turning direction of the photosensitive drum with a specific gap between the electron generating devices and a surface of the photosensitive drum. The LED arrays are disposed against outer ends of the electron generating devices opposite to inner ends thereof facing the photosensitive drum. When activated by a driving circuit according to image information, individual LED elements of the LED arrays emit light, causing the electron generating devices to emit electrons in a pattern corresponding to the image information. The electrons emitted from the electron generating devices produce more electrons due to an electron avalanche phenomenon before reaching the photosensitive drum, eventually forming an electrostatic latent image on the surface of the photosensitive drum.