A developing device applicable to an electrophotographic copier, facsimile transceiver, laser printer or similar image forming apparatus and having a developing roller for carrying a nonmagnetic single component type developer, i.e., a toner and a toner supply roller for supplying the toner to the developing roller. The developing roller has dielectric portions and conductive portions each having a small area and distributed together on the surface thereof. The conductive portions are connected to ground and have a volume resistivity of 10.sup.6 .OMEGA.cm or below. The toner supply roller is made up of a metallic core and an elastic foam layer provided on the core and having conductivity and a predetermined frictional charging characteristic. A potential difference is set up between the developing roller and the toner supply roller to generate electric fields which act on a frictionally charged toner as a force directed from the toner supply roller toward the developing roller. Micropores existing in the surface of the toner supply roller have a depth and a size selected in such a manner as not to disturb microfields formed by frictional charges deposited on the dielectric portions. The two different kinds of electric fields exist together to enhance the supply of charged toner. To eliminate leaks between the two rollers, one of the rollers is semiconductive while the other roller is conductive, and use is made of a toner whose resistance is greater than predetermined one.