A transport roll 1 consists of a metal roll 3 of 40 mm in diameter covered with a conductive PFA tube 2 of 10.sup.10 .OMEGA.cm in volume resistivity and 200 .mu.m in thickness. A DC voltage source 4 is connected to the metal roll. A sheet of paper 5 bearing toner images 6 and 7 on both sides thereof receives a drive force from a paper drive roll, and turns with the movement of the paper. The DC voltage source produces voltage VB1 of the same polarity as the charging polarity (positive) of the toner image 6 being in contact with the transport roll. The voltage VB1 is optimumly controlled so as to prevent the transport roll from being soiled with toner.