Bubbles in working fluids have much influence on the performance of fluid power systems. One of the authors has developed a novel device for bubble elimination capable of eliminating bubbles and decreasing dissolved gases using swirl flow. In this paper, performance of bubble removal in oil flow is studied through numerical analysis of the swirl flow in the device. This paper also documents a reduction of oil temperature rise and removal of entrained air from the working fluid in the hydraulic circuit by use of the device. It has been confirmed that the device is effective keeping the oil temperature low in the fluid power system.