To perform the sealing processing to an outer wall face without disturbing the mounting and demounting of a hood body in a ventilation tool composing an outer wall part of a ventilation hole for communicating an indoor side of a building and the outside air.

This ventilation tool is composed of a mounting plate 1 provided with a cylindrical part 11 inserted into an outer wall-side conduit in a ventilation passage communicating the indoor and outdoor sides and a collar part 12 abutted on an outer wall C, and the hood body 3 covering a lower opening. An edge of the collar part of the mounting plate 1 is bent (14, 15) to a cylindrical part side, a recessed part and a screw hole for burying a head part of a wall fixing screw are formed on proper parts of the collar part, and the hood body 3 is provided with a flange part 32 corresponding to the collar part of the mounting plate to expose the bent edge 15 of the mounting plate, and has a threaded hole corresponding to the screw hole.