A thermal-transfer printing apparatus includes a roll-paper-supplying unit that rotates an image-receiving paper roll and unwinds and winds a roll type of first image-receiving paper, and a print unit that includes a thermal head for heating a thermal transfer sheet and that forms an image by transferring a color material from the thermal transfer sheet to the first image-receiving paper. With the image-receiving paper roll removed, a reverse unit that reverses a sheet type of second image-receiving paper is mountable in a region in which the image-receiving paper roll used to be contained. The print unit forms the image on the first image-receiving paper in a first printing mode in which the image-receiving paper roll is contained in the region, and the print unit forms an image on both surfaces of the second image-receiving paper in a second printing mode in which the reverse unit is mounted on the region.