A belt pretensioner for a safety belt comprises a pyrotechnic propellant charge (34) able to be operated by a fuze (48) and adapted to act on a drive device for a belt pretensioner. The drive device comprises a piston (18), adapted to be moved in translation, of a piston and cylinder unit. The pyrotechnic propellant charge (34) is mounted within the extent of a cylinder space (28) enclosed by the piston and cylinder unit. The fuze (48) is designed in the form of a self-contained unit and arranged separately from the propellant charge (34).