1. An image forming apparatus for printing a display image serving as a printing target for display on paper with color material, comprising: a printing surface mode determination section configured to determine whether or not a printing surface of the display image is simplex printing; a printer configured to print the display image on a first surface of paper in a case of simplex printing; a display image analysis section which analyzes a printing range and a density of the display image; a curl suppression image determination section configured to determine, if the display image is simplex printing, a printing position and a printing pattern of a curl suppression image for suppressing a curl of the paper caused by the display image based on an analysis result of the display image analysis section; and a curl-preventive image addition setting section configured to set image information of the printing position and the printing pattern of the curl suppression image which is determined by the curl suppression image determination section and is to be printed on a second surface of the paper, wherein the printer prints the curl suppression image with color erasable material.