Abstract: Two identical differential mechanisms are mounted in parallel between the input shaft connected to the rotor 1 of the wind generator by a speed step-up device, and the output shaft connected to a synchronous generator. The two planet gears are secured to the output shaft. The two planet carriers are secured to the input shaft. The two annulus gears therefore rotate at the same speed. They are connected by slightly differing transmission ratios, of which one is also reversing with respect to the other, to the two input elements of a comparator differential. The cage of this differential rotates at a speed equal to half the difference between the absolute values of the rotational speeds of the elements. After multiplication by gearing, this low speed is applied to the rotor of a regulating apparatus such as an electric generator. The transmission ratio is adjusted or regulated by altering the torque applied by the regulating generator.