An image forming apparatus including; an image carrier carrying a toner image; a transfer belt making pressure contact with the image carrier through a sheet of paper and transferring the toner image onto the sheet of paper; a plurality of supporting rollers stretching and supporting the transfer belt; and a transfer roller to which transfer electrical current is applied, as well as making pressure contact of the transfer belt with the image carrier from a back surface of the transfer belt, wherein at least one roller of the supporting rollers is formed in an inverted crown shape with a size of the center portion is smaller than a size of the end portion, and the transfer belt is rotationally driven for a prescribed time without applying transfer electrical current both or in either of before and after transfer of a toner image.