An image forming apparatus includes a belt to transfer a printing medium, a plurality of support rollers which rotatably supports the belt, a photosensitive medium which has a surface on which a visible toner image is formed by charged toner, a transfer roller which is disposed adjacent to the photosensitive medium with the belt interposed therebetween, a power supplying part which supplies power to the transfer roller so that a surface of the transfer roller has an electrical potential, and a control part which controls the power supplying part to supply a pulse power, which has a middle power of a same polarity as a polarity of the charged toner, to the transfer roller so that the charged toner remaining on the belt after the belt transfers the printing medium past the photosensitive medium is transferred back to the photosensitive medium.