PURPOSE: To form a high-quality image with excellent intermediate gradation reproduction properties and color reproduction properties, by uniformly exposing a photosensitive body to light the quantity of which is approximate to a minimum effective light exposure for a photo-curable substance, prior to imagewise exposure.

CONSTITUTION: The illuminances and exposure times of uniform-exposure light sources 1, 2, 3 respectively for yellow, magenta and cyan are so set that the light exposures become respective minimum effective light exposures for the colors. Light reflected by a manuscript 12 irradiated with light from an imagewise-exposure light source 4 is focused on a photosensitive body 8 by a lens 5 to perform exposure. The imagewise exposure is so controlled that the sum of the light exposure in uniform exposure in each individual color by a filter 13 disposed near an aperture diaphragm for the lens 5 and the light exposure in a highlight area of an image becomes a maximum effective light exposure. By this, it is possible to obtain a copied image or printed image having well-regulated hues and high image quality while retaining gradation information on an original image.