To provide a simple ventilation and interval keeper in a single swing ing door, by which a door of a vestibule of a multiple dweling house or the like intercepting the ill ventilated interior from the exterior can be formed in consideration of crime prevention and with satisfactory ventilation function to be air ventilated.

A panel 1 is formed to have the same height as that of a vestibule door and an arbitrary width, and the panel 1 is provided with plural air holes 3 between an insecticidal net 2 is stretched. An angles locking piece 4 is provided on one end part of the panel 1, and the locking piece 4 is provided with plural oblong holes 5 having a round hole 5a at the lower end. The other end of the panel 1 is provided with a contact piece 6 which is angled in the same direction as or in the opposite direction to the locking piece 4 and abutted to a door stop of the frame of the vestibule door.