Abstract
Stirling coolers using refrigerants, such as helium, which have no impact on the depletion of the ozone layer and global warming attract a great deal of attention because they take effect on the environment problem arising on a terrestrial scale. The authors developed the Stirling cooler for the ultra-low temperature region used with the equipment for vacuum, biomedical and so on. This paper discusses the durability test of the Stirling cooler which achieved the cost decrease and the performance improvement by optimizing a structure and driving condition aiming at practical use was evaluated. It is clear that an increase in the contaminative element of the working gas inside is related as one of causes to with the performance deterioration.