Abstract: The structural base unit of the machine is made of a one-piece shaped beam (40) which extends along a first direction (Y) with a first portion (41) which, due to its own stiffness, supports and guides the carriage (12) carrying the writing head (11) along its translational motion in the first direction (Y), and with second and third portions (45) which defines supporting surfaces for the drum (20) driving the printing medium in a second direction (X) perpendicular to the first direction (Y). Guiding of the carriage (12) is ensured by rails (43, 44) formed integral with the beam or attached to it, and a slot (50) cut in the shaped beam (40) along the action area of the writing head for providing a passage for the printing medium and its engagement with the drum (20).