PURPOSE: To prevent the occurrence of rotting fungi and moldering of construction material under the floor by providing the top of a continuous footing with a plurality of recesses constituting slit ventilation ports under base.

CONSTITUTION: Outside air is introduced into underfloor space 12 through a mothproof net and a ventilation port 11 fitted with an outside air intake adjusting board provided at the concrete continuous footing 2 of a building by temperature difference between outside and inside and natural wind pressure. Here, since the air in an in-wall ventilation layer 5 goes up, being warmed by the temperature rise of outside air or solar heat, the air introduced into the underfloor space 12 is taken in through the slit ventilation port 3 under the base, and passes through the ventilation layer 1A, and passes a cut ventilation groove 10A, and is sucked in through a cut ventilation port 4A, and is introduced into an in-wall ventilation layer 5, and updraft is generated continuously. And, the updraft passes the cut ventilation groove at the uppermost part of the wall and is introduced into attic space, and is discharged to outside by an ventilation device attached to the uppermost ridge of the building.