A planetary roller screw mechanism includes a screw shaft provided with at least one external thread, a nut provided with at least three internal threads and at least three rollers arranged, radially with respect to a central axis of the screw shaft, between the screw shaft and the nut. Each roller is provided with at least two external threads. The number of external threads of the screw shaft is a multiple of the number of external threads of a roller. The number of internal threads of the nut is a multiple of the number of external threads of a roller.