An arm drive mechanism which rotates an arm, an angle sensor which detects a rotation angle of the arm drive mechanism and outputs angle information, an angular velocity sensor which is attached to the arm, detects angular velocity acting on the arm and outputs angular velocity information, a control command generating unit which outputs a control command value prescribing a rotational operation of the arm, a gain adjusting unit which incrementally or decrementally changes and thus adjusts a gain of the angular velocity information, and an arm operation control unit which controls an operation of the arm based on the control command value, the angle information and the gain-adjusted angular velocity information, are provided.