To stabilize developing characteristic, to prevent the deterioration of an image due to an excess current and to eliminate the occurrence of developing ghost by making the average volume particle size of developer formed on a developer carrier after developing a black image and that after developing a white image have specified relation.

The average volume particle size of the developer carried on the developer carrier when the developer is formed to a layer having specified layer thickness by a developer supply member again after the black image is developed is defined as Dbk. The average volume particle size of the developer carried on the developer carrier when the developer is formed to the layer having the specified layer thickness by the developer supply member again after the white image is developed is defined as Dwt. At such a time, they satisfy the relation of Dwt/Dbk>0.8. By controlling and restricting the difference of the volume average particle size between a black image developing part and a white image developing part to be within a specified range, the change of average specific charge amount depending on an image pattern can be held within a fixed value, so that the developing ghost is prevented from occurring and excellent development is performed.