To provide a connection structure high in airtightness, liquidtightness, and connection stability between a cylindrical member such as a metal tube and a connected object thereto, and connect the cylindrical member to the connected object with less number of parts and working steps and simplified manufacturing technology.

The tip edge of the cylindrical member 20 such as the metal tube is folded to the outside, and the inner peripheral surface of the folded piece 21 is brought into contact with the outer peripheral surface of the cylindrical member 20 such as the metal tube. The outer peripheral surface of the folded piece 21 is set to dimensions allowing it to be connected to the inner periphery of an opening part 23 in the connected object 22. The tip of the folded piece 21 is bent and projected in a direction crossing the axial direction of the cylindrical member 20 such as the metal tube to form a flange part 24. The flange part 24 is fixed to the outer peripheral surface of the connected object 22.