Abstract: The invention relates to an automatic continuously variable positive mechanical transmission, making it possible to avoid using a hydrodynamic torque converter and a switchable gearbox. A planetary unit (44) linking an input shaft (30), transmitting a working torque CM, to an output shaft (31) transmitting a load torque CR. A reaction torque RC resting on a fixed point (35) of the case is added to the working torque in the planetary unit (44) via two successive planetary centrifugal devices (36, 37) with eccentric weights. The second centrifugal device (37) permanently balances the three torques CM, CR and RC. The first centrifugal device (36) transmits the reaction torque CR to the second which it sets using a setting of the eccentricity for its weights. Such a transmission can drive the output shaft at a continuously variable speed between zero and a speed equal to or greater than that of the input shaft. It is applied to driving vehicles or variable speed machines.