The purpose of this study was to analyse the throwing motion biomechanically. The throwing motions of forty pitchers were investigated by a 3D motion capture system using seven CCD cameras. Thirty-three reflected markers were applied to each joint and body landmark of a pitcher for taking the images. The angle, velocity and accelerated velocity of each joint were measured with these data. The reactant force was calculated by using a simulated model. The turning point of these planes was identified ”TOP’’ in this study and also the ”TOP’’ position showed the maximum rotated position of the trunk. The velosity of an elbow joint accelerated from the ”TOP’’ position to the MER. And decelarated from the MER to releasing a ball. The direction of a resultant force indicated the anterior of the shoulder joint during the phase between the ”TOP” and the MER, a glenoid between the MER and releasing a ball, and a posterior of the shoulder joint after the releasing a ball.