An image forming apparatus includes a transfer device to transfer an image on an image carrier to a transfer sheet. The transfer device includes a transfer roller and transfers an image on the image carrier to a transfer sheet conveyed into a transfer area between the transfer roller and the image carrier by applying a bias voltage to the transfer roller. The transfer device includes a device to apply a release agent for an alien substance to a surface of the transfer roller. Toner and an alien substance, such as paper dust, thereby hardly adheres to the release agent applied on the surface of the transfer roller. Even if toner and/or an alien substance are put on the release agent applied on the surface of the transfer roller, such toner and/or an alien substance are easily removed by a cleaning device. Thus, lowering of an image quality due to insufficient cleaning of the transfer roller is avoided.