PROBLEM TO BE SOLVED: To improve an effect to prevent a fish from intruding into a water intake even in a place where a power source is difficult to secure.SOLUTION: A fish intrusion prevention device to prevent a fish from intruding into a downstream side of a water intake 8 comprises: a propeller 5 which is arranged at an upstream side of the water intake 8, provided with a color disliked by a specific fish, and rotatable by water flowing toward the water intake 8； and a float 2 which is connected to the propeller 5 and movable in a vertical direction in accordance with a change in a water level of the water flowing toward the water intake 8. The propeller 5 is constantly positioned at a predetermined depth in relation to a water surface of the water flowing toward the water intake 8 following a movement of the float 2.
