PURPOSE: To reduce the cost of construction work by a method in which a movable contactor is erected on a float on water surface near a separate gate in water touched by the gate of the levee, and a motor is normally or inversely turned by contact of the contactor to the fixed contactors on the upper and lower stages.

CONSTITUTION: In a movable levee to be opened or closed by vertically moving a gate, a water surface 27 to be shut down or led to water surfaces 28 and 30 in contact with a gate near the gate by opening or closing a water conveyance path 29 is provided. A movable contactor 36 is erected from a float on the water surface 27 and interposed between fixed contactors 24 and 25 of upper and lower stages, erected from the top of the gate. By contacting the contactor 36 to the fixed contactors 24 and 25, the motor 11 for winding up or down is turned normally or inversely. The top of the gate is vertically moved as the float 34 goes up or down in such a way as to keep a fixed distance between the height of the levee to be closed and the level of the water surface 27. The movement of water in the tidal current sensor of the river can thus be regulated by a small device.