To provide a mechanism capable of maintaining the effect of separating mixture and a transportation capacity even if a transportation path of sediment containing the mixture becomes longer.

Dredged soil sucked by a separation and transportation device 14 is separated into mixture and sediment contained in the dredged soil while the dredged soil is transported inside a pipe body 140 by a gas-mixing jet. At this time, auxiliary nozzles 148 provided in the pipe body 140 blow air from a wall surface of the pipe body 140 to strengthen a force of the gas-mixing jet. Therefore, the effect of separating the mixture by the gas-mixing jet and a transportation capacity can be maintained even if the length of the pipe body 140 is long. The separation and transportation device 14 discharges the dredged soil into a mixture removal device 13 through an exhaust port 143. When the dredged soil is injected into the mixture removal device 13, the mixture remains in a space formed by a net-like member 130 and the sediment passes through the mesh of the net-like member 130 and drops downward by gravity.