A fin structure for heat-exchanging, the fin structure being mounted on a heat-dissipating portion of a Stirling cycle cooler, wherein the fin structure is configured by coupling a plurality of unit structures, the plurality of unit structures being split by a plurality of surfaces extending from a inner circumference of the fin structure toward an outer circumference thereof. The fin structure is configured thus way, whereby it can be mounted on the heat-dissipating portion so as to sandwich the heat-dissipating portion from the outer circumference thereof by the plurality of unit structures coupled one another. Accordingly, when mounting the fin structure, large force is not required, no adhesive filler is applied to an unneeded portion of the Stirling cycle cooler, and generating a scratch or a distortion on the casing of the Stirling cycle cooler can be prevented.