An endless belt transports a recording medium through image forming sections and transfers toner images from corresponding ones of the image forming sections onto the recording medium. The endless belt has a surface resistivity and a volume resistivity. The surface resistivity and the volume resistivity are related such that 0.3.ltoreq.(log .rho. s-log .rho. v).ltoreq.1.3 where .rho. s is the surface resistivity in .OMEGA./.quadrature. measured after a voltage of substantially 500 V is applied to the endless belt for ten seconds and .rho. v is the volume resistivity in .OMEGA.cm ten after a voltage of substantially 250 V is applied to the endless belt for ten seconds.