A fusing device is provided for use in an image forming apparatus to fuse a toner image having a polarity on a printable medium. Such a fusing device comprises: a heating roller which comprises a heat source; a driving roller which is spaced apart from the heating roller; a fusing belt which travels on the heating roller and the driving roller and is heated by the heating roller; a pressing roller which forms a fusing nip against a surface of the fusing belt and presses the printable medium to the fusing belt; and a power supply which applies a voltage to the pressing roller to electrify the printable medium into a polarity opposite to the polarity of the toner image.