Abstract: A friction-wheel speed reducer for machines rotating at high speed of rotation of the epicycloidal double train type employing between a drive rotor (2) and the output shaft (3) of a driven rotor the mechanical drive effects by rotary friction which are obtained by the rolling of friction wheels which are strongly applied against each other. The forces of application are generated by the centrifugal force resulting from the orbital rotation of mass planetaries (5) of mass (M) and propagated from wheel to wheel up to the drive rotor (2) via outer planetaries (6) provided with wheels (62) on the rim of which they rest, the said outer planetaries (6) being disposed to roll while resting on circular tracks (10) via their bearer hubs (61), the movement of rotation being captured by the side cheeks (31) of a planetary-holder cage (30) and transmitted to the output shaft (3) with which it is integral.