<p>In this paper, we proposed a concept of supporting human reaching motion using a branching robot arm system. The proposed robot system comprises a long-reach arm robot with a small arm attached. We primarily focus on the mechanism and control method of the small arm. The small arm incorporates proximity and force sensors and can follow a person’s arm in real time or continue to generate a constant support force. Through participant experiments involving tasks related to fetching an object at a certain height, we confirmed that the proposed system can achieve these tasks. In addition, by varying the degree of assistance, we significantly reduced muscle load. Furthermore, we obtained insights into appropriate tasks and support conditions from the perspective of other muscles and muscle fatigue reduction. We also confirmed the applicability of the proposed system to the subject of object manipulation against a vertical wall as an applied task of reaching.</p>