PURPOSE: To change the height of a weir.

CONSTITUTION: Guide posts 2 are erected on both sides of a water channel 1, and a gate body 5 is fitted slidably into grooves in the vertical direction. Approximately one third on the upper side is notched while leaving lug sections on both sides in the gate body 5, and an upper gate 7 having a shape and size adapted to the notched section is mounted on the gate body by a pin 9. The upper gate 7 is rotated around the pin 9, and can be tilted. Fan-shaped plates 11 are extended toward the downstream side from the lug sections of the gate body so as not to form a clearance between the upper gate 7 and the gate body 5 when the upper gate 7 is inclined. A wire rope 13, a root of which is fixed onto the eyepiece of the upper gate 7, is passed through guide sheaves 15 installed to the gate lug sections, and further wound on the drum of a manual winch 17 through guide sheaves 16 on beams 3.