A dust removing mechanism in two steps, i.e. dust sweeping and pressing, is employed. While paper is on the conveying belt, the dust on its on surface is swept away by the hairbrush roll and brush row, removed by suction fan and run over by an electric heating pressing roll. In this way the dust depositing on paper in printing is effectively removed. Furthermore, paper can be accurately transported without any back-off or dislocation using the compact arrangement and design of the conveying belt in combination with effective air suction.