In a printer of the type in which printing is carried out on a recording medium with a print element through an ink ribbon interposed between the print element and a sheet or paper, a ribbon cassette accommodating therein the ink ribbon has a ribbon stopper removably provided for limiting the movement of the ink ribbon within the ribbon cassette. A switch is provided for detecting the presence of the ribbon stopper in the ribbon cassette when the ribbon cassette is mounted on the printer. If the ribbon stopper is detected by the switch, then a ribbon feed motor is not energized so that the ink ribbon is not withdrawn from the ribbon cassette. Thus, the ink ribbon will not be cut off, which may otherwise be caused if the ribbon is forcibly withdrawn without removing the ribbon stopper.