In recent years, the development of the in-vivo medical devices are remarkable. Generally, in-vivo devices need the internal battery. The life of internal battery is limited, and the maintenance of the battery is necessary. For overcoming this problem, the ultrasonic wireless power transmission technology is studied. In the past reports, the transducer of ultrasonic wireless power transmission system is not designed for electrical matching with input source, amplifier circuit, and rectification circuit, etc. In this paper, we propose the efficient ultrasonic wireless power transmission system. For realizing the efficient system, the impedance matching between the input source, amplifier circuit and the ultrasonic transducer is considered. And the optimum position of two transducers necessary for achieving a high transmission efficiency is searched. Moreover, the voltage booster circuit to obtain the high DC oputput voltage is designed. In the transmission experiment, it is confirmed that the high DC output voltage for the operation of the in-vivo devices is achieved.