PURPOSE: To provide a duct mounting and removing mechanism with which the opening of a duct is butted with the opening of a part to be connected and then connection is generated with removabilily by a very simple operation and a very short period of time.

CONSTITUTION: The opening of a duct 2 is butted with the opening of a part to be connected 3 and then connection is generated removably. The base end of bellows 11 is fixed to the tip of the duct, and a swinging member 13 is mounted near the bellows swingably with the middle part as fulcrum. A guide 15 is provided with which one end of this swinging member is detained with the tip of the bellows while the other end is contacted with the part to be connected. The guide is equipped with a slope 15b inclining relative to the opening of the duct. The secondly named end of the swinging member is guided while in contact with the slope to put the swinging member into rotation, and the firstly nazed end of the member moves the tip of the bellows as approaching and going apart from the part to be connected.