In this paper, we propose a method to estimate impact forces from accelerations, and confirrm effectiveness of this method using simple models and marketing models. First, we measure frequency response functions of golf clubs by the experiment with an impulse hammer. Then, we really strike balls with a robot for striking and estimate the impact forces for different conditions of head speed and characteristic of balls. Finally, we calculate impulse of impact forces to evaluate consistency of estimated impact forces quantitatively and show that estimated results are effective for characteristic of golf clubs and balls.