To more effectively suppress failure of reduction in heat exchange efficiency caused by adhesion of frozen moisture on a surface on a low temperature gas flow passage inlet side of a core part, by a simple configuration.

This air conditioning system includes: a high temperature gas flow passage 4 in which high temperature gas is made to flow; a low temperature gas flow passage 5 in which low temperature gas is made to flow; a condenser 6 which serves as a heat exchanger and has a first core part 6a used for performing heat exchange between the high temperature gas and the low temperature gas and a second core part 6b arranged on the upstream side from the first core part 6a in the high temperature gas flow passage 4, having a main passage for making the high temperature gas flowing within the high temperature gas flow passage 4 pass through and an auxiliary passage for making temperature control high temperature gas having a higher temperature than that of the high temperature gas within the main passage pass through, and used for performing heat exchange between the gas within the main passage and the gas within the auxiliary passage; and a high temperature bypass flow passage 7 branched from the high temperature gas flow passage 4 and communicated with the auxiliary passage of the second core part 6b.