To suppress a resistance of flow, facilitate maintenance, and surely eliminate foreign matter from the seawater.

A water tank 4 for sprinkling the seawater to a heat transfer pipe 1 of a carburetor by overflow is disposed adjacently to the heat transfer pipe 1, it is set that the seawater flows in one direction in the water tank 4, a screen 11 formed by arranging a train of many stays at a constant clearance is disposed in the water tank 1 in a gently erecting state with respect to flow of the seawater, and a bucket 15 for collecting the foreign matter is disposed on an upper end part of the screen 11.