Self-winding watch

A self-winding watch, said watch including a frame, comprising:

• a self-winding mass having a central part surrounded by raceways of a ball bearing, one of which is integral with said central part and another of which is integral with means for positioning and means for removably fastening to the watch frame, a reduction gear train for connecting the self-winding mass to a barrel arbor and a reversing mechanism to convert the two-directional rotational movement of said self-winding mass into a one-directional rotational movement, transmitted to said barrel arbor, wherein two first pinions of said reversing mechanism are freely pivoted, concentrically with said central part, each of the first pinions meshing with a planet pinion, the pivot pin of which is integral with said central part and the toothing of which is shaped so as to allow only unidirectional rotations of s aid first pinions in two opposed respective directions of rotation, the first pinions being integral with two second respective moving parts of said gear train, the directions of rotation of which are opposite, one with respect to the other.