A strap driving device for a strapping machine comprises an insertion-return unit; a tensioning unit; and guide channel portions for the strap which lead toward the device for inserting, returning and tensioning the strap and away from said device, with the guide channel portions being provided with cheeks guiding the strap along both sides of its flat sides, wherein rollers on one side of the insertion, return and tensioning unit and the cheeks of the guide channel portions are mounted preferably stationarily on the same side while the cheeks of the guide channel portions on the other side are mounted on a movable carrier which is displaceable, by means of an actuation device, between a working position with closed pairs of rollers and guide channel portions and a service position with open pairs of rollers and guide channel portions.