Ultrasonic vibration systems consisting of an exponential horn and a terminal rod are analyzed by the finite element method. The influence of the length and the shape of the rod on the vibrational mode and on the resonant frequencies of the systems are made clear, and these results agree qualitatively with the experiments. The results of these studies offer to guide for designing ultrasonic vibration. Further, these studies enable the removal of the limits of application of ultrasonic vibration (i. e., ultrasonic working, ultrasonic fatigue test, ultrasonic surgical knife for operation etc.).