To provide an animal invasion-preventing weir having a simple mechanism, capable of preventing the invasion of animals into a specific place in a river area and further making driftwood, etc., to flow toward the downstream without damming the driftwood, etc.

This river weir for preventing the invasion of animals is formed by vertically disposing main pillars 1 on both the sides of a river in a mutually faced state, inserting a support bar 5 into the pipe of a weir body 6 comprising the pipe having a proper length and fine rods continuously disposed on one side of the pipe, spanning the combination of the weir body 6 with the support rod 5 between the main pillars, suspending the fine rods to bring into contact with the bottom of the river, and disposing the weir body 6 in a state capable of being rotated on the support rod 5 in a constant direction.