PURPOSE: To perform printing without regulating the interval between a head and printing paper corresponding to the thickness of paper by a method wherein a carriage is struck against a paper-thickness detecting plate when it moves to the end part of the printing paper, while a support block mounting the printing head is fixed on the carriage.

CONSTITUTION: A supporting block 4 is pressed in the direction of a platen 8 by a spring 5 and, while a projection 7 thereof being kept in contact with a cam 10 and a paper-thickness detecting plate 6, a carriage 3 is moved slidably in the direction of an arrow (b). By this, resisting against the pressure of a spring 12, the slant- formed tip of the detecting plate 6 comes into contact with printing paper 9. When the carriage 3 moves and the tip of a printing head 1 moves also to the end part of the printing paper 9, a fixed device 11 such as an electromagnetic clutch is energized, the contact point thereof touching the surface of the carriage 3 and thereby the supporting block 4 being fixed to the carriage 3. By this, the printing head 1 is fixed in accordance with the thickness of the paper 9 and the interval (g) between the tip of the head 1 and the paper 9 is maintained.