PURPOSE: To enable stable output to be delivered even if a prime output device which is violent in energy fluctuation, is applied by controlling tha controlled output of a motor and the like in a continuously variable transmission having a planetary gear type reduction mechanism.

CONSTITUTION: A windmill 2 rotating at low speeds where the pitch angle of the windmill can be controlled, is connected to the input shaft (d) of a continuously variable transmission 1. A generator 3 is connected to an output shaft (a'), and a control motor 4 with a brake is connected to a control shaft (e'). A carrier (g) is set at the end of the input shaft (d), a plurality of planetary gears (c) are rotatably provided for the carrier (g), so that the planetary gears are meshed with both a sun gear (a) and an internal gear (b) in such a way that the planetary gears can be rotated, and is also freely revolved around sun gear (a). Moreover, an external gear (f) is formed integrally with the internal gear (b), and a control gear (e) meshed with the external gear (f) is fixed onto the inside tip end section of the control shaft (e'). By this constitution, the gear ratio and the rotational direction of the output shaft (a') can easily be changed by changing the number of revolutions of the control shaft (e').