To provide a rain water cutoff member capable of being installed in a vent opening connected to the outdoor side by opening in the below and preventing the incursion of rain water into the vent opening and, at the same time, ensuring the circulation of air in a rain water cutoff member preventing rain water from entering the vent opening.

In the rain water cutoff member 1 provided to a coping vent opening connected to the outdoor side by opening in the below and preventing the incursion of rain water into a coping vent opening, it has at least two rotational spiral or at least double circular cross section, it is equipped with a cylindrical body 5 placed at right angles to the direction of a watercourse of air passing through the coping vent opening, and a plurality of small holes 6a and 6b penetrating through the direction of the radius are formed in the cylindrical body 5.