PURPOSE: To provide the titled cassette enabling to fit and detach a heat transfer printing material speedily and securely, wherein a said material is enclosed in a casing so that an intermediate part of the material is exposed, and the casing is provided with a slit along the axial direction of winding cores which slit is opened on one end side.

CONSTITUTION: A heat transfer printing ribbon cassette 14 comprises two parallel winding cores 31, 32, and a thermal transfer ribbon 15 is enclosed in the casing 33 so that an intermediate part thereof is exposed to be intermediately located between a platen and a thermal head. Between winding core containing parts 33a, 33b of the casing 33 is provided the slit 34 along the axial direction of the winding cores which slit is opened on one end side, and driving force receiving end parts 31a, 32a for the winding cores 31, 32 are provided on the side of the opened end of the slit 34. Accordingly, the exclusive space required for fitting the heat transfer printing material is reduced.