PURPOSE: To form an image by detecting an insertion area from the image information of an original and to generate the image information of external information, thereby forming the image of the image information after the synthesis and synthesizing the image to the prescribed position of the original easily and accurately.

CONSTITUTION: At first an area discrimination means 12 extracts an area where external information is inserted from an image density of the image information of an original read by preliminary scanning by a scanner 11. Succeedingly, the inserted areas are rearranged in a prescribed order and the external information is inputted from an external information input means 2 to a control section 13, the input external information is corresponded to the insertion area and expanded in a font RAM 15. Then the scanner 11 is used to make scanning and the image information of the external information is synthesized onto the image information of the read original by a synthesis circuit 17 and the synthesized information is outputted to a printer 18. Thus, the image information of the original and the external information are synthesized with a simple operation to form an image.