Abstract: A self-winding watch includes a self-winding mass having a central part surrounded by raceways of a ball bearing. One raceway is integral with the central part. Another raceway is integral with means for positioning and means for removably fastening to watch frame. A reduction gear train for connects the self-winding mass to a barrel arbor. A reversing mechanism converts the two-directional rotational movement of said self-winding mass into a one-directional rotational movement. Two first pinions of the reversing mechanism freely pivot, concentrically, with said central part. Each of the first pinions meshes with a planet pinion. The pivot pin is integral with the central part and the toothing is shaped so as to allow only unidirectional rotations of said first pinions in two opposed respective directions of rotation. The first pinions are integral with two second respective moving parts of the gear train, the directions of rotation of which are opposite, one with respect to the other.