To suppress inconvenience that a low temperature air flow passage is closed through the deposition of a freezed moisture content on an inlet side surface of a low temperature gas flow passage of a core part without preparing a particular member for melting the freezed moisture content 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.

A condenser 7, i.e., the heat exchanger provided with the 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 further includes a low temperature side inlet duct 7d, i.e., a low temperature gas stream guide means for introducing the gas circulated in the low temperature gas flow passage to the core part 7a while guiding the freezed moisture content contained in the gas circulated in the low temperature gas flow passage to the upstream side of the high temperature gas stream indicated by an arrow X on the surface as shown by an arrow Y on the inlet side surface of the core part 7a.