Abstract: A device measuring air permeability of a building, including: an airtight duct, open at both its ends; a motorized fan; an air induction member positioned in the duct with its axis of rotation substantially parallel to a longitudinal axis of the duct; a mechanism measuring pressure difference between an inside of a part of the building and an outside of the building; an adjustable shut-off member shutting off the duct, and configured to vary locally cross section for air flow through the duct, the shut-off member being continuously adjustable between a configuration of minimal shutting-off of the duct and a configuration of complete shutting-off of the duct; and a mechanism determining a degree to which the duct is shut off by the shut-off member for a reference pressure difference determining, from the degree of shutting-off, either corresponding air flow rate through the duct, or a parameter representative of the air permeability.