To provide a ventilation device which can be set on an outer wall and can ensure indoor-outdoor ventilation without power consumption.

An overhang plate part 34 provided to overhang from the outer wall 12 includes a pair of side openings. A projection-like member 23 projecting toward an opening 13 is provided on the inner surface of the overhang plate 34. Wind flowing along the outer wall 12 is taken through one side opening, and carried while bypassing the projection-like member 23 before being derived through the other side opening. In this case, the downwind side over the top 23a of the projection-like member 23 becomes a negative pressure area with a generation of negative pressure. The indoor air is drawn into the negative pressure of the area C.