An image-forming device includes a photosensitive drum, a conveying unit, a transferring roller, an optical sensor, a ground connector. The photosensitive drum carries a developer image. The conveying unit includes a driving roller, and an endless belt. The endless belt is disposed in confrontation with the photosensitive drum and transferring roller. The optical sensor is disposed near the driving roller and detects the developer image on the endless belt. The first connection member has a first electrical resistance and is connected between the driving roller and a ground connector electrically grounded. The second connection member has a second electrical resistance and is connected between the endless belt and ground connector. The first electrical resistance is less than the second electrical resistance so that an electrical charge is quickly removed from the driving roller and more gradually removed from the endless belt, thereby simultaneously preventing adverse effects on image formation and adverse effects on the optical sensor disposed near the driving roller.