PURPOSE: To avoid an identification mark from being visibly recorded when a copied substance is an original in a device where copying is performed by adding the identification mark which is not visible.

CONSTITUTION: The density histogram of a yellow image signal used to record the identification mark among color image signals obtained by reading the original is formed (S1). When the ratio α of the number of picture elements included in the density range of the identification mark to the number of all the picture elements (S2) is equal to or above a fixed value (S3), it is decided that the identification mark is included in the image of the original (S4). When the identification mark is included in the original, the density of the yellow signal of the pixel included in the density range of the identification mark is set to zero and the information of the identification mark is eliminated (S5). Thereafter, image processing such as color change and variable power, etc., is performed and then the information of the identification mark is newly added to perform recording.