Drive device for a wind mill comprising a large pulley (21) disposed on a main shaft (22) and at least one belt (27) or chain adapted to transfer rotation from the pulley (21) to a generator (30, 31). The pulley (21) is rotationally coupled to at least two secondary shafts (23, 24), which are disposed parallel to the main shaft (22). One or more belts (27), which transfer the rotation, extend over the pulley (21) and the secondary shafts (23, 24). The secondary shafts (23, 24) are in turn rotationally coupled to at least one, preferably two, electric generators (30, 31).