To provide a countercurrent plate fin type heat exchanger capable of reducing heat conduction via a structure material from a high temperature side to a low temperature side and improving heat exchange efficiency, and an air cycle refrigeration system for a container capable of improving refrigeration capacity by improvement of the heat exchange efficiency.

In this heat exchanger for heat release or heat exchanger for heat recovery as the countercurrent plate fin type heat exchanger, heat insulating materials 21 for blocking heat conduction in a flow passage flowing direction via plates 20 and heat conduction fins 19 are provided in a plurality of sections in the flow passage flowing direction of a heat exchanger body.