To accomplish satisfactory image quality with reference to a high resolution original image by setting a developing condition by taking the charge dispersion of a latent image due to the leak resistance of a ferroelectric carrier into consideration.

Provided that the electrostatic capacitance of the ferroelectric carrier is expressed by Cp (F/m2), a surface resistance is expressed by Rs (Ω), a time up to a finish of developing after forming the electrostatic latent image is expressed by t (sec), the non-image part potential of the electrostatic latent image in an image area when forming the electrostatic latent image is expressed by Vo (V), the surface voltage of the carrier when starting a developing operation by a developing member with a saturation latent image potential for a solid image is expressed by Vth (V) and a desired minimum image width is expressed by W (m), and the limit latent image potential for the minimum image width is expressed by V1 (V), and when the potential V1 is controlled so as to establish the following expressions; V1=(0.348Wr2-1.161Wr+1.0163)Vo and Wr=(1/3.63)×(Rs×Cp/t)1/2×W, abs (V1)<abs (Vth) is established (provided that abs (X) is set as the absolute value of X).