To prevent suspended matters such as ice piece from flowing into a branch passage even if the ratio of an intake flow rate to a river flow rate exceeds 50%.

In this device, a floating body structure is composed of a plate-like object of uniform width Bw having a first plate-like part 34 and a second plate-like part 36 integrally formed continuously with the first plate-like part. The first plate-like part is formed to place its main plane orthogonally to the water surface of a main stream of a river, to incline the main plane with respect to the stream direction of the main stream of the river and to fix one end 20 on the opposite side to the second plate-like part to the side upstream of the position of an intake 30 in a sidewall surface in the main stream of the river. The second plate-like part is formed to place its main plane orthogonally to the water surface of the main stream of the river and to set the main plane parallel with the stream direction of the main stream of the river.