We analyze the pitching motion in early cocking phase, focusing on pronation restriction which causes pitching disorders. In consideration of disorders to develop in the elbow joint inside, we devise the parallel mechanism that simulated forearm skeletal system briefly. Furthremore, we suggest the estimated technique for pronation supination (pro-/supination) angle of the narrow sense and the rotation center axis vector using the motion capture system in order to evaluate pro-/supination in pitching motion analysis. It can apply to the posture estimation of other joints to estimate the rotation center axis vector with the posture change of the pro-/supination. As a result, the pronaton restrictuions were not seen in the subject, but confirmed elbow which fells down. This is caused by the fact that the kinetic chain between forearm pronation, elbow flexion and stretching up of arm was non-efficiency. Therefore, considering the results, it is necessary to clarify this kinetic chain between these motons, we will confirm the fact by increasing number of the subject.