To provide a sediment inflow prevention device for a channel which automatically closes a water intake when a water level rises to prevent sediment and stone from flowing into a channel while allowing water to be continuously taken.

A sediment inflow prevention device for a channel comprises: a plate-like gate 10 capable of closing a water intake 101 of a canal 100; a pair of right and left connection bars 41 which are rotatable and connect side faces of the gate 10 and upper portions of a canal; a pair of right and left props 21 which are rotatably connected to frontal side faces with lower edges thereof placed on upper surfaces 105 of the canal; and a collision plate 51 which is placed across lower portions of the pair of right and left props. The gate 10 has through-holes 11 which prevent sediment and stone from flowing into the canal 100 while allowing water to be taken. When a water level rises and water current pushes the collision plate 51, the gate 10 supported above the canal 100 with the props 21 as well as the connection bars 41 is fallen down to close the water intake 101.