A thermal transfer printing apparatus includes a reading device for reading a code registered section provided on an ink sheet cassette, and a color discrimination device, a part of which is provided on a thermal head. The apparatus acts to heat an ink sheet superposed on a print paper by means of the thermal head to print an image on the print paper. The ink sheet cassette includes a pair of ink shafts on which both ends of a continuous ink sheet having a continuous film or paper with inks applied thereon are wound, and a cassette case in which the ink shafts are received, at least one of the ink shafts being adapted to be drivingly connected in the axial direction to a torque supply shaft inserted from the outside of the cassette case so that driving torque is supplied from the torque supply shaft to the ink shaft. The code registered section is composed of a first pattern portion of alternating white and black patterns and a second pattern portion in which information connecting the ink sheet is coded and recorded in line with the first pattern portion. The code registered section is provided on one of the ink shafts in the cassette case.