To reduce a time and labor required for operation by diverting water from a weir to a plurality of snow flowing ditches by a simple operation and to provide a diversion gate permitting safe passing by eliminating dangers of falling accidents of passengers or passing motor vehicles into the weir.

A door body 9 is fixed to a bearing portion 8 installed to a weir 7 in a freely rotating manner in a horizontal direction inside the weir 7, the door body 9 is turned and moved by operating a handle from above the grating 1, and the door body 9 is locked to an opening 6 connected to the first snow flowing ditch 4 of the inner wall of the weir 7 and a predetermined position apart from the opening 6 connected to the second snow flowing ditch by operating the handle from above the grating 1 to turn and move the doorobody 9. Thus, water can be diverted easily by adjusting and diverting the amount of water to the first snow flowing ditch 4 and the second snow flowing ditch 5 by a simple operation without opening a grating 1 and without requiring an operator to enter the weir 7.