In the golf, the flying distance and direction of ball just after impact is influenced by various motions of the golfer's rotation and translation, the sidespin and initial velocity of the ball, the motion club head and so on. Since the cock motion is done in the near point of contact of the body and the club. It is noticed as the position which transmits the energy stored in the rotation of the body to the club. In this paper, we proposed the measurement method and it's system for using the gyro sensor in order to measure this motion. Although the method was developed for cock motion measurement in the golf swing, it can be applied to baseball, tennis and so on.