PURPOSE: To prevent occurrence of contamination of paper with ink by adjusting a gap between a printing head and a platen.

CONSTITUTION: A platen 2 supported by bearings on side plates 1 is rotated by a paper feed motor 7 through gears 6, 8. A printing head 3 is provided on a guide shaft 12 disposed parallel to the platen. An ink ribbon 4 is set between the platen and the printing head. A sensor 20 for detecting contamination of paper with ink is provided on the printing head. On a signal outputted from the sensor, a control means not shown by a figure drives the printing head and connects the drive gear 6 with a connection gear 13 of the guide shaft through a clutch gear 16. The guide shaft 12 is rotated by the rotation of the connection gear 13. A gap between the printing head 3 and the platen is adjusted to be too large to contaminate paper with ink by moving the printing head up and down by an eccenric shaft part 12a of the guide shaft 12. Since a memory circuit is connected to the control means, the printing head can be always positioned at an optimum position.