PURPOSE: To enhance the reliability of reading accuracy of an ID sensor and print quality by providing a brush arranged on the side frame side so that it comes in contact with a ribbon protector, and a calculation device which calculates the printing duty of one line when printing is effected on a medium.

CONSTITUTION: A brush 15 is fixed to a bracket 16 provided on a side frame 13 in the extension direction of a platen 1, and when a carriage 2 moves to a position where the brush 15 is arranged, the tip of the carriage 2 comes in contact with the rhombic hole part of a protector 6. Ink sticking to the ribbon protector 6 is removed under the above configuration. In addition, a calculation device calculates the printing duty of one line, and if the calculated value is higher than a specified level, the device issues a command by which to move the carriage 2 to a position for the brush 15. Further, during an action to read an ID mark, the device allows the surface of the ID sensor 14 to be cleaned, unless the sensitivity of the ID sensor reaches a specified level. Thus it is possible to prevent print quality from becoming worse due to print contamination.