Abstract: Projections are formed on the tip end part of a pipe for directly fitting the pipe into a capsule without using any extraneous elements, thus providing an economical and firmly fitting mechanism. Such a structure is commonly used in a heat exchanger. A tank includes a capsule formed into a box shape with one side open and a bottom panel disposed at the upper and lower ends of a heat exchanger and brazed thereto. A pipe fitting hole is formed in a side panel of the capsule, and around the pipe fitting hole is concavely formed a ring-shaped part inside the tank, and around the-ring-shaped part is formed a cylindrical part approximately at a right angle to the plane of ring-shaped part. On pipe is formed a flange part, and on a tip end part of the pipe are formed projections.