To provide a device capable of separating and removing dust in an oil/water separation vessel allowing only formation of a slight height difference of the water level within it.

A dust trap 1 has a supporting plate 10 being long in the vertical direction and having a back surface facing the wall surface and a porous trap portion 20 constituting a space for dust collection on the front-surface side of the plate 10. The plate 10 has an opening 13 for the incoming flow formed in its upper part, and the trap portion 20 extends from the lower part of the plate 10 to such a height as to cover at least the whole of the opening 13. The trap 1 collects the lower- and the higher-specific-gravity dust separately, and the lower-specific-gravity dust moves vertically with the varying water level, thereby preventing choking due to an increase of the flow rate in an oil/water separation vessel with only a slight height difference of the water level.