PURPOSE: To stably and easily replace an ink ribbon by continuously providing a first cutout for mounting a reel and a circular arc-like second cutout for rotatably holding the reel in an ink ribbon unit using by refilling an ink ribbon.

CONSTITUTION: In the ink ribbon unit for replacing contained to be refilled in an ink ribbon cassette comprising a removable upper case, and a lower case unit assembled with a member for supplying and winding an ink ribbon and the like, a supply side ribbon spool 5 obtained by winding the ribbon on a supply air (reel) 6 is contained in a ribbon case 7 mad of a sheet or the like. The case 7 has a cutout 61 having a circular arc-like cutout 61a and a substantially parallel cutout 61b in such a manner that the an inner diameter D of the cutout 61 is larger than a profile of a shaft 62 of the core 6 and smaller than a profile of a collar of the shaft end, and the core 6 is inhibited to be removed.