In a line head, a plurality of element arrays arranged in a first direction. Each array includes a plurality of light emission elements arrayed in a second direction which is perpendicularly to the first direction. The light emission elements emit light for forming an electrostatic latent image on a photosensitive surface of an image carrier. A switcher activates the light emission elements in at least one of the element arrays while deactivating the others. A developer develops the latent image as a visible image with toner.