The cost of utilizing kinetic energy of river stream, tidal and ocean current is considered to be higher than that of wind power generation because of difficulties in construction and maintenance of devices installed in seawater. As a solution to the problem, the authors propose a new concept of water stream turbine. The main idea is in the manner of supporting turbine. Although it is similar to a vertical axis turbine, the direction of turbine axis is not firmly fixed and its tilt angle is passively adjustable to the stream velocity. Since it does not have to keep the turbine axis in upright position, required structural strength and weight of the device will be reduced significantly. This paper describes the application ranging from the small hydro power in river streams to large application of tidal and ocean current turbine. In the large capacity plant for tidal stream and ocean current, the main mechanism of turbine axis support is the same as that of the wind turbine authors proposed in the previous paper. It leads to the further opportunity of cost reduction. The sample design of a multi-megawatt ocean current turbine shows the possibility of high economic performance of the concept. The results show that the cost of energy in the concept can be comparable to a land based wind turbine.