Hydraulic systems have features of compact and high output power. However, in recent year, further downsizing and higher output power of hydraulic equipment have been demanded. As a result, operating pressure of hydraulic systems has been increasing and cavitation has significantly occurred with increasing pressure. The purpose of this study is to reduce the cavitation occurrence by eliminating bubbles in oil in high pressure condition. In this paper, the relation between the amount of the cavitation erosion and the bubble elimination is experimentally investigated.