To provide a thermal transfer printer whereby a detection mark of an ink sheet can be shortened, the structure can be simplified and the number of components can be reduced, and an ink cartridge.

This thermal transfer printer thermally transfers an image on an image-receptive sheet such that an ink sheet having a plurality of ink sheet sections in a plurality of colors arranged in area sequence is moved relative to a thermal head to carry out sub-scanning. The thermal head 51 is integrally equipped with sensor sections 58, 59 for detecting a detection mark for detecting completion of the sub-scanning with respect to each ink sheet section.