Abstract: An instantaneous direction changing rotation mechanism in which its driving shaft and driven shaft have coincident central lines, the driving shaft can be controlled for transmission via either a direction changing train of gear with negative train value or casing of gear for driving the driven shaft for rotation in either reverse or normal direction; the intermediate bevel gear of the train of gear has a spindle extending to the exterior of the casing of gear and fixed to a brake block so that the above control can be achieved by engaging or disengaging the brake block with a barke element; a movable ring is surrounding the upper part of the casing of gear so that while the rotation of the movable ring is restricted by the sensor means, there is an angular displacement against the casing of gear for disengaging or engaging the brake element with the brake block.