A thermal transfer printer having simpler structure, occupying less installation space, and enhancing the user convenience. The thermal transfer printer includes a cartridge having print paper wound in a roll, a capstan roller for conveying the print paper by applying frictional force on the print paper, a printing head for printing images on the print paper, and a platen roller for selectively pressing the print paper against the printing head. The housing of the cartridge has a first opening penetrating the housing and extending laterally. A paper roll case is rotatably installed in the housing and has a second opening penetrating the paper roll case and extending laterally. Inside the paper roll case, a paper roll is stuck on the inner surface of the paper roll case, and print paper is wound from the inner surface of the paper roll case to inward direction, while a first end of the print paper is exposed through the second opening.