A tensioning drive for a safely belt device. The tensioning drive includes a gas generator, a drive wheel and a supply pipe which connects the gas generator and the drive wheel. A plurality of pushing members is included in the supply pipe. The pushing members are accelerated after the gas generator has been activated. The pushing members drive the drive wheel, and at least one of the pushing members completely or at least partially seals the supply pipe. The sealing action of the at least one sealing pushing member is ended or reduced after a predetermined distance has been travelled.