A non-contact type of developing device for use in an image forming apparatus having an image forming body, includes a developer conveying body facing the image forming body in which a magnet body having a plurality of magnet poles are attached therein, to convey two-component developer in the form of a developer layer onto a developing area and a control electrode provided at the developing area or upstream of the developing area. The control electrode has an electrically insulating member which is in contact with or close to the developing layer, and an electrode to which a voltage is applicable is attached to the insulating member. The following condition is satisfied: ##EQU1## where D.sub.T represents a number of toner layers on the assumption that the toner particles passing through the developing area are filled most densely, D.sub.WS represents a conveying amount (mg/cm.sup.2) of the developer layer at the developing area on the developer conveying body, T.sub.c represents a toner concentration (%) in the developer, dt represents an average sphere equivalent diameter (.mu.m) of toner in the developer, .rho.t represents a toner density (g/cm.sup.3) in the developer, vs represents a circumferential speed (mm/s) of the developer conveying body at the developing area, and vp represents a circumferential speed (mm/s) of the image forming body at the developing area.