Using a high speed video and computer system, the baseball pitching motion of shoulder was analyzed with in Nobuhara Hospital. The data cames out as three dimensional motion characters, motion angle, speed and position translation. The result shows the shoulder works as both the fulcrum and connecting point of pitching arm. During the pitching motion, the resistance force, weight of the pitching arm and the contraction force of muscles set up a combination force along the pivot of the humerus. All the forces passing through the glenohumeral joint become stress and shearing force working at the shoulder structure, which depending on the contacting angle of the humeral pivot and glenoid surface. During the accelecration phase the pitching arm seems as a third class lever system. The elbow extension will elongate the resistance arm of this lever and add an extraforce to the shoulder. The tension force will become bigger on the anterior and Posterior part of shoulder, if the motion plan of the shoulder flexion moved horizontally.