PURPOSE: To obtain large buoyancy in no relation to the material of a water turbine, by connecting a driven machine of generator or the like with the floating movable water turbine and providing a gliding plate, tilting diagonally downward in the waterstream direction and sinking in the water, in a supporting part of the water turbine as a buoyancy mechanism.

CONSTITUTION: A casing 7, serving as a supporting part for water turbines 6, 6, fixes a rod 8 in the front end so as to be extended to the upstream side. Said rod 8 mounts to its front end a hydrofoil 9 in a sideward position in a side of the right bank 2. While a fixed side for the casing 7 mounts a gliding plate 10 in a manner tilting diagonally downward in the flow direction of water and sinking in the water. The hydrofoil 9 generates a lift component in the perpendicular direction for canceling antitorque of a generator 5 while in the horizontal direction for placing a hydraulic power device in the center of a river, while the gliding plate 10 serves as a buoyancy mechanism floating the water turbines 6 and the generator 5.