PURPOSE: To dam up, regulate and discharge water according to the amounts of water by vertically moving a float and an intake door provided inside a water tank whose water level is moved verticaly through small holes in directly opposite direction between a beam and a frame by means of a rope provided through a fixed pulley.

CONSTITUTION: When the amount of river water is increased, a float 2 is raised, a fame 6 is dragged by an inside rope 8, an outside rope 8 is loosened, and an intake side door 4 is lowered. Also, when the float 2 is lowered, the frame 6 is dragged by the outside rope 8, the inside rope 8 is loosened, and the intake side door 4 is raised. When water level is raised by heavy rain, etc., water is maximumly released at the upper limit of the main stream side door 3, and the intake side door 4 is lowered and landed on the bottom of river or lake. When the amount of water is reduced, the main stream side door 3 is lowered and the intake side door 4 is raised.