Abstract: [Object] To enable further improvement in user convenience. [Solution] Provided is a robot arm apparatus including: an arm unit made up of a plurality of links joined to each other by one or a plurality of a joint unit, the arm unit being connectable to an imaging unit; and a drive control unit that controls driving of the arm unit by causing each joint unit to be driven cooperatively. The drive control unit uses relative position information of a reference position with respect to the arm unit, the relative position information being based on a state of the arm unit and distance information about a distance between the imaging unit and the reference position, to control the driving of the arm unit in a manner that the reference position is positioned on an optical axis of the imaging unit.

Abstract: [Object] To detect a rotational angle accurately and also to drive more safely. [Solution] Provided is an actuator (300) including: a reduction gear (320) that reduces, by a certain reduction ratio, a rotational velocity of an input shaft joined to a rotary shaft of a motor (360), and transmits the reduced rotational velocity to an output shaft (350); a first absolute angle encoder (330) that detects a rotational angle of the input shaft; and a second absolute angle encoder (340) that detects a rotational angle of the output shaft.