PURPOSE: To prevent the occurrence of water flooding at the water flooding period by securing the effective area of river by a method in which the axis of a water- turbine power generator provided in a cell type main gate is parallelized with the vertical direction, and an outlet port is formed in the lower part of the outside plate on the downstream side of the main gate.

CONSTITUTION: A vertically movable cell type main gate 2 is provided between dams 1 provided at an adequate interval along the widthwise direction of a river, and an intake port 3 is formed in the upper part of the outside plate 2' on the upstream side of the gate 2. A discharge port 4 is also formed in the lower part of the outside plate 2' on the downstream side. A cylindrical water-turbine power generator 5 whose axis is parallelized with the vertical direction is provided in the main gate 2, and a water conveyance tube 6 through which the inlet and intake port 3 of the power generator 5 are connected and a suction tube 7 through which the outlet and discharge port 4 of the generator 5 are connected are also provided. The water turbine of the generator 5 is turned by water coming into the water conveyance tube 6 from the intake port 3 to generate power and then discharged from the port 4 through the suction tube 7. Since the generator 5 is provided inside the gate 2, the effective area of river can be sufficiently secured and the water flooding can be avoided during the flooding period of river.