PURPOSE: To fully exhibit a spurn water effect while maintaining ventilation efficiency.

CONSTITUTION: A duct for ventilation set up on a vehicle is provided with a frame 1 in which a exhaust port 13 is formed for exhausting air inside of a compartment to the outside thereof, a tabular flap 2 which is mounted outside of the compartment of the frame 1 in such a manner as covering the exhaust port 13 and then being opened only in the direction to the outside of the compartment by a pressure difference between pressures inside and outside of the compartment; and a spurn water 3 which is formed in a cylindrical to shape on the back compartment side of the frame 1 communicated with the exhaust port 13 and which has a height of 1.2 times exhaust port heights a1, a2 or more.