PURPOSE: To connect the suction duct of an engine simply and certainly with an extension duct for the atmosphere by making this connection of two ducts through a cylinder, which consists of an elastic material and is provided on the peripheral surface with a plurality of flare-shaped parts in small wall thickness.

CONSTITUTION: One end of a suction duct 8 whose other end is leading to the air cleaner of a car engine is connected with one end of an extension duct 10, whose other end opens to the atmosphere, through a cylindrical member 11 made of an elastic material. At the ends of the peripheral surface, this cylindrical member 11 is provided with a plurality of flare-shaped parts in small wall thickness 11b, and also in the central part with a higher small wall thickness part 11c. The two ducts 8, 10 are fitted to the small wall thickness parts 11b at both ends until they contact the small wall thickness part 11c in the center. Thereby the small wall thickness parts 11b at the ends are put in tight contact with the inner surfaces of the ducts 8, 10, and their connection can simply and certainly be made even though their relative positions are in eccentricity.