A device for transmission of rotary motion and transfer of a fluid medium, comprising a planetary gear train for transmission of rotary motion about a main axis which has at least one reduction stage which is provided with a sun gear, which rotates about the main axis, and a toothed ring gear which are mutually concentric and between which at least two planetary gears are engaged which are supported in rotation at least about the respective longitudinal axes which are parallel to the main axis by a planetary gear carrier; such planetary gear train is provided with a driving input sun gear and with an output ring gear and with an output planetary gear carrier, of which one can move in rotation about the main axis with respect to the other; and a rotary joint which extends externally to the planetary gear train for transfer of the fluid medium.