In order to investigate the effects of gravity center position of golf club head on the behavior of club shaft, deformation of shafts while a golf swing was simulated by the finite element method. As results, the following two points are obtained. Firstly, after the top of swing the deflection of the tip position of the shaft is enlarged by the bending moment caused by the centrifugal force due to the off-centered gravity center of club head from the shaft axis. Secondly, the longer the distance from the impact face to the gravity center of club head becomes, the larger the deflection of the tip position of the shaft is generated with the larger bending moment caused by the centrifugal force.