An image forming apparatus includes a developing device having a photosensitive element rotating in a given direction to form a latent electrostatic image on a surface thereof through a laser scanning unit, and a developing roller developing the latent electrostatic image into a toner image using a developer, a transfer part transferring the toner image onto a transported printing paper disposed on a paper-transporting path to engage the photosensitive element, and a subsidiary transfer part having at least one light source disposed on at least one of both sides of the paper-transporting path to expose the photosensitive element to light and thereby to enhance a transfer efficiency, and an optic fiber guide disposed longitudinally along the photosensitive element to lead the light generated from the light source to the photosensitive element.