PURPOSE: To effectively ventilate the under part of a floor of building and the roof space, by forming a lengthwise hollow part connected to a collective stack body by a horizontal hollow.

CONSTITUTION: Dew is prevented from being condensed in an exhaust vent 4 since humidity does not come into the vent 4 from a collective stack body 2, by providing a space 4A between a lengthwise exhaust vent 4 and a hollow tube 2A. Besides, there is a sucking action in a lengthwise hollow 6, which is communicated with the collective stack body 2 by a horizontal hollow 6A. The under part of a floor and the roof space can be ventilated, since the under part of a floor 7A and the roof space 7B and interconnected to the above-mentioned hollows. As a result, the generation of humidity, which is harmful to a building, can be prevented.