Abstract: An ink ribbon cassette is pivotably mounted to a printer. Ink ribbon is accommodated in the ink ribbon cassette and is caused to travel by a ribbon feed roller driven by a drive shaft provided in the printer. Printing operation is carried out at the cassette end arm portion by a printing head, while the cassette end arm portion is reciprocatingly moved in the widthwise direction of the ink ribbon relative to the fixed printing head by an actuating mechanism so that a printing region of the ink ribbon is diffused and becomes wider than a printing width of the printing head. The actuating mechanism includes a small gear integral with the ribbon feed roller, a cam driven by the small gear, and a lever engaging with the cam.