In a printer, a drive motor, a drive roller arranged on the shaft of the motor, a reversal roller in spaced relation to the drive roller, and an elongated drive belt trained about the drive and reversal rollers form a tensioning device, the belt being fastened at its ends to a print-head carriage for selectively displacing the carriage in the forward and reverse directions along and relative to a printable substrate support roller or base. The reversal roller is carried in a carrier housing which movably and cooperatively engages a spring-loaded tensioning wedge for maintaining the elongated drive belt in a predetermined tensioned or stretched relation. In order to avoid the need for a separate or specialized drive motor and an additional drive belt for advancing an inked printing ribbon, the drive force for the inked-ribbon drive shaft is derived from the reversal roller which, in the normal operation of the printer, is rotatable in opposite directions for selectively positioning the print-head carriage along the printable substrate support. For this purpose, a clutch member is interposed between the reversal roller and a gearwheel associated with the inked-ribbon drive shaft, the clutch member being longitudinally movable into coupled and uncoupled relations with the inked-ribbon gearwheel as a function of the direction of rotation of the reversal roller.