PURPOSE: To enhance airtightness against the effects of noises and high winds by improving the corrugated shape, thickness, and the like of a bellows-shaped self-supporting membrane which is mounted between two consecutive vehicles and which hermetically protects a passage for intercommunication between the vehicles.

CONSTITUTION: A self-supporting membrane 3 mounted between two consecutive vehicles 1, 2 is secured to the end faces of the opposite vehicles by means of locking flanges 4, 5 provided at both ends thereof and hermetically protects a passage for intercommunication between the vehicles 1, 2. Such a membrane 3 is formed into successive corrugations of increasing depths from one end to the other. The thickness of the membrane 3 which is roughly constant along the middle corrugation is increased along the shallowest corrugation 19 and the deepest corrugation 9. Further, the top of each corrugation appearing in close proximity to the outer surface F of the membrane 3 is formed to have a remarkably increased thickness in relation to the roughly constant thickness of the middle corrugation by the addition of a shape made of an elastomer compound forming an excess thickness portion 23.