When sub-images are sequentially transferred and connected together to form a larger image than would be possible with a single transfer operation, the occurrence of a color change in the overlapping region of the sub-images is suppressed and the width of the overlapping region is reduced as much as possible. Color image data are divided into image data of two sub-images containing an overlapping region and having edges that coincide for each color ink transferred to paper. Color values of the color image data in the overlapping region are converted by using a color conversion factor group created in advance for each position on the overlapping region so as to cancel out a color change that occurs in the overlapping region when the sub-images are transferred with one overlapping the other. The image data of the sub-images are corrected by adjusting converted color values in the overlapping region by using a correction factor for print density at each position on the overlapping region. A color image is formed by sequentially transferring the sub-images in accordance with corrected image data thereof so that the sub-images overlap at the overlapping region.