To devise a automatic fluid transmission stout, simple in structure, reduced in fuel consumption and rapidly manufacturable by automatically increasing/decreasing a rate for supplying oil to a driving axle continuously arranged dynamic oil forcibly deliverying mechanism.

As a static pressure hydraulic mechanism, an output is controlled by the magnitude of a force pressurizing cross section. Namely, a dynamic oil forcibly delivery rotary gear rotator 2 is operated through a power transmission shaft 7 by a prime mover 1. An oil rate is increased/decreased by a pressure sensitive oil level regulator 3, and its operating prime force is supplied branching from a dynamic oil forcibly supplying pipe 8. A secondary power generation rotary gear rotator 4 is rotated by the pressure oil so as to drive a load shaft 6. Oil completed an operation is entered into a pressure sensitive oil regulator 3 bypassing a return pipe 9. In this case, the magnitude of inner pressure correspond rapidly at the time of traveling on a ground and a slope. When a load becomes large a pipe passage opening/closing valve in a regulator 3 interlocked with advance of a piston is shifted to a closing side.