To protect a heat exchanger tube of a heat exchanger made of a ferrite material against embrittlement.

In a heat exchanger particularly for utilizing waste heat in a chemical industry wherein a heat exchanger tube made of a ferrite material and having one end thereof pressure-tightly secured to an inside of at least one hole of a tube plate is provided and the heat exchanger tube is arranged in a heat exchanger housing through which cooling medium is made to flow, protector tubes 6 made of a material having a good resistance against embrittlement, e.g. Cr-Ni steel, are arranged at least in the heat exchanger tubes 3 in a high temperature range and the protector tubes are secured to the range of the tube plate 4 in the heat exchanger tube 3 by liquid pressure expansion.