PURPOSE: To set a hood with a required minimum projection margin regardless of varying thickness of wall of a building and avoid impairing the appearance of the building, by providing a hood with a mounting frame which can be slid forward and backward and with a connector for connecting and fixing the hood, and providing a flashing frame at an exterior wall surface along the periphery of the hood.

CONSTITUTION: In mounting a ventilating fan in place, a hood 4 and a mounting frame 8 are inserted from the interior side, and a flange 7 of the frame 8 is fixed to a wall surface by screws or the like. The hood 4 is slid relative to the mounting frame 8 so as to adjust the outside projection margin of the hood 4 to an appropriate value, and the hood 4 is fixed by a connector 10. A flashing frame 5 is fitted over the hood 4 from the exterior side, and a flange part thereof is fixed by screws or the like. The outside projection margin A of the hood 1 can be adjusted to an appropriate value, regardless of varying thickness B of wall of a building, so the appearance of the building is not impaired. The connector 10 is not limited to a screw, and may be any other means that can couple and fix the mounting frame 8 and the hood 4 to each other.