PURPOSE: To obtain an image where parts of two colors are separated clearly at their boundary part by developing a 1st image with high-brightness toner and a next image with low-brightness toner.

CONSTITUTION: A latent image with high brightness which is formed on a photosensitive drum 4 is developed by a toner developing device with high brightness and transferred to copying paper supplied from one of stack parts 13W15 and the transfer paper is stored in an intermediate tray 33. A latent image with low brightness which is formed on the drum 4 is developed by a low-brightness toner developing device 7 into a visual image, which is transferred to the copying paper so as to overlap with the image with slightly high brightness at the boundary part. Thus, those toner particle which differ in brightness are used to obtain the color image where the boundary parts are clearly separated.