PURPOSE: To stabilize two latent image potentials and to form an image with stable color tone by irradiating light which has different illuminance for a different color and performing electrostatic charging to a potential lower than uniform charging, and thus forming two latent images for different colors.

CONSTITUTION: The photosensitive body 1 consisting of a conductive substrate 11 and a photoconductive layer 12 is charged uniformly and electrostatically by a corona charger 2. Then, the photosensitive body 1 is irradiated with image light I from an original image. The image light I contains two light components; and bright light corresponding to the 1st information, e.g. black has the quantity EL of light and dark light corresponding to the 2nd information, e.g. red has the quantity EM of light. Then, electrostatic charging is performed to a potential nearly equal to a potential VM obtained by irradiating light to a potential lower than uniform charging, i.e. the quantity EM of light after the exposure of the light I. Consequently, two stable latent images VL and VM are formed and developed with toner particles of black and red. Consequently, the potentials of the latent images of the different colors are stabilized to form a two-color stable image.