To provide a thermal transfer printer in which movement of a ribbon cassette is regulated when it is inserted into a cassette loading section so that an ink ribbon does not rub on a surrounding member nor the position of the ribbon cassette is shifted even if a vibration, or the like, is applied externally.

The thermal transfer printer P comprises a ribbon cassette containing an ink ribbon 14 in the body section, a frame having a section for loading the ribbon cassette removably, and a thermal head cantilevered by the frame. A cassette guide part for regulating the movement of the ribbon cassette being inserted into the cassette loading section in the direction perpendicular to the inserting direction of the ribbon cassette is provided, respectively, at the cassette loading section and the ribbon cassette.