The present invention relates to a Self-Governed Gear Box (SGGB) functions as an automatic gear box system suitable for any power drive ranging from electrical to mechanical. This is an optimally-performed gear box system, in terms of power loss. The assembly is compact and simple with no additional elements other than gears. For the same reason, it is highly economical, easy to assemble and easy to maintain, with an expected ideal performance. Such a dynamic task of an automatic gear box system is achieved by implementing an algorithm enabling to sense the additional load applied at the input end, created by diverting a small quantity of power from the output end. This is in effect of inducing an engine disturbance as under-drive, under sub-optimum output rpm-torque conditions. As the engine disturbance introduced for sub-optimum output rpm-torque condition is a continuous governance mechanism, the input to output speed ratio assumed also will be continues in a designed range. The engine starts from zero speed when this gear box system is coupled between an engine and a load. Thus it is a continuously variable transmission system.