HEAT EXCHANGER

PROBLEM TO BE SOLVED: To provide a heat exchanger capable of immediately transitioning from a non-use state to an use state by preventing aged deterioration of heat transfer tubes disposed in the heat exchanger for a long period to the use of the heat exchanger.SOLUTION: A heat exchanger 100 is a multitubular heat exchanger having a plurality of heat transfer tubes 104, and exchanging heat between high-temperature steam flowing inside of the heat transfer tubes 104, and low-temperature outside air (air) flowing outside of the heat transfer tubes 104. The heat transfer tube 104 is covered with a protective film 105 so that its outer surface is not exposed to the outside air. The protective film 105 is made of a material sublimating by the flow of high-temperature steam inside of the heat transfer tube 104.