Owing to huge amount of kinematic energy, ocean current has the potential to be a base power source, it's also source for huge and steady flow energy. Moreover, Japan has potential ocean area -which can be used for large scale power production. One example is Kuroshio which is one of the strongest ocean current. However, since the flow velocity of a steady ocean current is low compared with the velocity of the tidal current, development of a system which can efficiently generate power in the low flow velocity is needed. Prototype testing is complicated because the area where Kuroshio current located is far from on shore. In this study, development of blades, water bearing, and a drive train suitable for a generation of electrical energy at the low flow velocity and towing test was carried out.