To minimize an overshoot and to realize high productivity by comparing the desired position signal and the actual position signal sent from a position sensor with a controller, multiplying the control signal by the error signal, and feeding it to a control valve.

A motor sensor 250 generates the motor position and/or speed signal in response to the rotation of a drive shaft 215, and a housing sensor 255 generates the housing position and/or speed signal in response to the rotation of an excavator housing 105 respectively. When a controller 240 receives these signals, it obtains the housing revolving speed and adjusts the control gain. The acceleration of the excavator housing 105 is grasped from the load state of a bucket. When the acceleration is slow, a low response control gain is employed. When the acceleration is fast, a high response control gain is employed to adjust inertial force. An overshoot is minimized for accurate positioning in any case, the machine performance is maximized, and productivity is increased.