To solve the following problem in a conventional rotary body which has high manufacturing and maintenance costs, troubles in self-servo properties, needed hydraulic-pressure, and fading, etc.

An oil pipe is connected from a delivery port of a hydraulic pump to a valve inlet, and the valve outlet and the suction opening are connected with the oil pipe to return to the original hydraulic pump. Thus, one closed circuit is made. Rotation of the rotation body to be controlled is transmitted directly or indirectly to a driving shaft of the pump, and rotation of the rotary body is controlled by regulating the stream of the oil by a variable valve.