PURPOSE: To eliminate a time loss of an image forming speed in case of using a photoreceptive sheet having high sensitivity by providing a means for setting document scanning speed and image forming process speed in accordance with sensitivity of the photoreceptive sheet, data of brightness of an image, etc.

CONSTITUTION: The control of a copying machine is executed by a CPU 11, and an exposure quantity and photoreceptive sheet carrying speed being image forming process speed are divided into set values of several stages and stored in a RAM 13. To the CPU 11, sensitivity of a photosensitive microcapsule, etc. based on a kind of photoreceptive sheet 3 and a manufacturing lot are inputted by a sensitivity input switch 14. Subsequently, in a state that the voltage of an exposure lamp 41 is held constant in accordance with sensitivity of the photoreceptive sheet 3, the document scanning speed and the image forming process speed are set. In such a way, even if a kind of the photoreceptive sheet and the manufacturing lot are different, a satisfactory image can be formed. Also, in case of using the photoreceptive sheet having high density, a loss of an image forming speed can be eliminated.