A pretensioner having a fracture connection-type rack gear, according to the present invention, comprises: a housing having a receiving space; a pinion gear which is provided in the receiving space, and which is connected to a rotation shaft of a spool having a seat belt webbing wound thereon, and is rotated by the rotation of the spool; a micro gas generator for generating explosive power in response to an impact from outside; a transport pipe, one end of which is connected to the micro gas generator, and the other end of which is formed with an opening so as to be connected to the receiving space; a plurality of ball members which are provided in the transport pipe, and which are transported to the receiving space by the explosive power of the micro gas generator; and a rack gear which is provided in the receiving space in a fixed state so as to be fixed by a fixing part, and which is engaged with the pinion gear as the fixing part is fractured by the ball members transported to the receiving space by the explosive power of the micro gas generator, and which rotates the pinion gear by means of the remaining thrust of the ball members in a direction in which the webbing is introduced.