An ink sheet damage calculating unit compares image element density data of each of areas into which an image is divided by an image area dividing unit with a first threshold to calculate the total number of pixels each having density data equal to or larger than the first threshold for each area, and then compares the total number of pixels calculated for each area with a second threshold. A printing operation selecting unit uses a remaining area of an already-used ink area for formation of a next print image when the total number of pixels is smaller than the second threshold in every one of all the areas, and uses an ink area in a new unit area for formation of a next print image when the total number of pixels is equal to or larger than the second threshold.