Abstract: The impulse variable speed device comprises an input shaft (2) and output shaft (2) both axially aligned. The input shaft is kinematically connected to a mechanism for converting rotary motion of the input shaft into an oscillating motion of an intermediate link. The output shaft is connected to a mechanism for converting the oscillating motion of the intermediate link into rotary motion of the output shaft, the mechanism comprising free-wheeling clutches and of heterodirectional action kinematically connected with the intermediate link. The mechanism for converting rotary motion into an oscillating motion comprises a bow-shaped guide rod fixed on the input shaft and having the center of curvature thereof on the axis of the input and output shafts and, which center is a single center of the variable speed device. A slider is put on said guide rod for displacement along the guide rod. The slider is pivoted to one end of a lever whose axis crosses the single center of the variable speed device.