Abstract: A thermal printer mechanism comprising an elongate support (1), a drive roller (4), a strip of print elements (3) mounted on said support, spring-forming means for urging said strip against the drive roller, at least one cam (5) mounted to pivot about an axis (A.sub.2) of the support (1) to move the strip (3) away from the drive roller (4), said mechanism being characterized in that it can be transformed from a stationary-roller version to a retractable-roller version, and in that the axle about which the drive roller (4) rotates is suitable for being selectively mounted either on the support (1), or on a paper-protecting cover (CP) hinged to said support (1), the cam of the stationary version being suitable for being replaced with at least one other cam suitable for being entrained by the paper-protecting cover being tipped up and vice versa.