To more efficiently suppress inconvenience that heat exchange efficiency is lowered through the deposition of freezed moisture content on an inlet side surface of a low temperature gas flow passage of a core part by a simple structure in a heat exchanger provided with the core part for performing heat exchange between the gas circulated in the low temperature gas flow passage and the gas circulated in a high temperature gas flow passage.

The heat exchanger includes a core part 7a for performing heat exchange between the gas circulated in the low temperature gas flow passage and the gas circulated in the high temperature gas flow passage, and a flow reversing means 9 for reversing the direction of the flow of the gas passing through the core part 7a.