The device according to the invention for tensioning and sealing of strapping bands has a band abutment (24) for the inner band edges (27) of the band ends (20, 21) to be welded together, which is provided with a band width adjustment device (28) according to the invention, with the help of which the band abutment adjusts the band abutment transversely to the longitudinal direction of the strapping band in the housing and that the device can be adjusted to strapping having with different widths without any reconstruction measures (see FIG. 3).