PROBLEM TO BE SOLVED: To ensure sufficient confidentiality, by determining appropriately a shape of a see-through preventive pattern, which makes image data of a manuscript hard to be visible, and a printing position while toner is saved, deterioration of a consumable part is prevented, and paper feed trouble is reduced. SOLUTION: An image data reading unit for reading image data formed on a manuscript, an image processing unit for carrying out region separation for a region, where effective information of the read image data is located, and determining a shape of a see-through preventive pattern and a formation position of the see-through preventive pattern for each region separated by the region separation, and an image printing unit for printing the determined see-through preventive pattern on a region corresponding to any of region, where effective information of the manuscript is located, on the rear face of a recording paper with manuscript, which was already printed, based on the information on the formation position of the determined see-through preventive pattern are provided. COPYRIGHT: (C)2009,JPO&INPIT