PURPOSE: To rapidly and efficiently execute character processing such as thickening by forming the outline image of image data and reading out and writing a synthetic unit data on a corresponding image to thicken or shadow the outline image.

CONSTITUTION: A CPU 1 to be driven by a program controls the whole system, an image memory is connected to a direct memory access (DMA) device 2 and both the CPU 1 and DMA device 2 can be allowed to access a common memory 4. The outline bit map of an original image 50 is formed at first, the outline bit map is read out in each plural picture elements and a prescribed bit map (synthetic unit data 62) is written on the position of the image 50 corresponding to the read picture elements by means of OR operation. In the case of shadowing processing, a prescribed slash bit map (synthetic unit data 62) corresponding to the direction and length of the shadow is written. The operation is executed in each plural picture elements of the whole outline bit map. Consequently, the thickening or shadowing of the original image can rapidly be executed.