A miniature cryocooler is used to reduce thermal noise in infrared sensors and laser analyzers. An infrared sensor is applied to industry, security and defense systems and space technology. Application to space technology has led the technology of cryocooler. In EOS-AM1 (Earth Observing System) by NASA, long-life (operating life 50, 000 hours that is 20 times longer than present one), low disturbance (0.1N that is 1/20 of present one) and low power consumption are required to the miniature cryocooler. These technologies have dramatically improved the miniature cryocooler. Here, the word “miniature cryocooler” means a cryocooler that works in 30-80K of cooling temperature and cooling capacity lower than about 1W. (1) Trend of R & D, (2) refrigeration principle, (3) stirling cycle cryocooler technology, (4) pulse tube are presented in this paper.