PURPOSE: To provide a heat exchanger which is easy in manufacturing, excellent in the thermal efficiency, and difficult in generating the stress fracture.

CONSTITUTION: An inner body 2 is concentrically arranged in an outer body 1 in the condition where the prescribed clearance is provided between the inner circumferential surface of the outer body 1 and the outer circumferential surface of the inner body 2, and both end openings of the inner body 2 are covered by a tube plate 3. A heat transfer tube 4 is pierced in the inner body 2 in the supported condition by the tube plates 3, a liquid inlet tube 5 and a liquid outlet tube 6 are projected from the inner body 2, a fitting hole is made in part of the outer body 1 opposite to the liquid inlet tube 5 and the liquid outlet tube 6, and the liquid inlet tube 5 and the liquid outlet tube 6 are fixed by a fixing means provided in each fitting hole.