PURPOSE: To provide the titled printing mechanism which can eliminate retreatment of a print head in the feeding of paper while eliminate a metal belt to be consumable part, by controlling the print surface of a print head to be kept constant by detecting the thickness of a printing paper.

CONSTITUTION: The thickness of a printing paper 6 in the advancing direction of the print head 3 is measured with a sensor 10 for measuring the thickness thereof 6 mounted on both ends of the print head 3 and the print head is controlled by the measured value to be maintained at a constant distance from the print surface. It is detected that the thickness of the paper varies from P1 to P2 as illustrated. When any change in the thickness occurs, the print head is lifted by the difference in the thickness with a print head lift mechanism 2 employing a DC motor and a stepping motor to keep the space between the print paper 6 and the print head 3. A printing paper holder 11 is made up of a spring whose part contacting the paper is made spherical.