To provide a heat exchanger improved in heat transfer efficiency.

In this heat exchanger which includes a plurality of flat tubes 1 arranged in parallel with each other to circulate a liquid inside thereof, and a plurality of cylindrical fins 4 respectively disposed between the plurality of flat tubes 1, and in which a gas is circulated between the plurality of flat tubes 1 along the extending direction of the cylindrical fins 4 to exchange heat with the liquid in the flat tubes 1, the cylindrical fins 4 comprise spiral portions 7 for generating swirling flow to the gas circulated between the flat tubes 1.