PURPOSE: To contrive the improvement of productibity and reliability as well as reduction of heat loss by a method wherein the discharging side of a heat transfer tube and the discharging pipe of second heat medium are penetrated through a specified place whereat a jacket between the inner and outer vessels is not provided and, further, the inner vessel is filled with particulated members.

CONSTITUTION: The specified place of the wall of inner vessel 22 or the outside of a lid body 25 is not provided with the jacket 23 while one end of the heat transfer tube 30 is penetrated through the lid body 25 and the discharging pipe 35 of high-temperature fluid is connected to the lid body 25. According to this method, only an introducing pipe inserting part 33 is connected to the inner vessel 22 and penetrated through the outer vessel 21, therefore, the assembled body of a heat exchanger main body 27 becomes separable from the outer vessel 21 and sealing works may be facilitated by a method wherein necessary places, such as connecting parts, penetrating parts or the like, are being sealed previously by welding or the like prior to the incorporation thereof and the connecting parts are sealed after the incorporation. Further, the heat transfer tube 30 is not penetrated through the inside of the jacket 23, therefore, leakage of low-temperature fluid as well as the thermal short-circuit between fluids may be prevented. The inner vessel 22 is filled with the particulated members 32, therefore, the flow of high-temperature gas becomes turbulent and the heat transfer performance may be improved.