In this paper, the effect of the swing form on the tennis elbow is discussed. It is commonly said that tennis elbow is caused by backhand stroke. However, many patients have elbowache during forehand stroke. The traces of swing were captured by video camera. From the equation of motion and the trace of the swing, the forces and moment at elbow and wrist were estimated. It was found that wrist has a large stress at the moment to decrease velocity of the forehand stroke. The smooth swing without rapid deceleration does not cause the stress. The moment on the throat of racket was measured by strain gages and the moment during forehand swing and backhand swing were discussed.