To enhance heat transfer coefficient at the downstream part of a heat transfer tube while preventing heat gas from passing between the heat transfer tubes.

The plate fin type heat exchanger comprises a plurality of juxtaposed heat transfer tubes 2 for passing a heat receiving fluid, and a plurality of plate fins 3 juxtaposed in the direction intersecting the plurality of heat transfer tubes 2 wherein heat gas g1 flows in a specified direction through a heat gas flow space S formed between the plate fins 3. The plate fin type heat exchanger is further provided with a fence 4 for introducing the heat gas g1 flowing through the side part of the heat transfer tubes 2 in the direction N orthogonal to the flowing direction F of the heat gas g1 passing through the heat gas flow space S to the peripheral part of the heat transfer tubes 2 on downstream side and then supplying the heat gas g1 to the downstream side.