To provide a novel heat exchanger which can greatly improve the life and reliability of a tube bundle in a heating fluid by removing a welded joint of the tube bundle.

Discharging and charging nozzles 12, 13 for fluid to be heated which flows through a tube bundle 17 are, respectively, provided in the vicinity of the top of a body 1. Individual heating tubes 30 consisting the tube bundle 17 are constituted with continuous tube members without welded joints. The tube bundle 17 is formed so that both ends of the individual heating tubes 30 are placed on the surface of the liquid of heating fluid. Both ends of the heating tubes 30 are connected to the individual nozzles 12, 13, respectively. In this way, the welded joints in the heating fluid are eliminated and thus the heating tubes are hardly influenced by the thermal stress, thereby improving the life and reliability of the tube banks.