PURPOSE: To increase the quantity of radiation from the high temperature end portion of a pulse tube by partitioning a passage portion in parallel to the central axis of the pulse tube.

CONSTITUTION: A pulse tube 8 is partitioned into passage portions 12, 12... parallel to the central axis of the pulse tube 8. In the compression process of this very low temperature refrigerator, a gaseous refrigerant compressed by the piston 3 of a compressor 1 is cooled while passing a precooling type heat exchanger 4, a cold accumulator 5 and a very low temperature end portion 7 and flows into the pulse tube 8. The gaseous compressed refrigerant which has flowed into the pulse tube 8 is fed with a pressure toward the high temperature end portion 10 and a halfway thermal diffusion to outside in a radial direction is prevented. As a result, a thermal gradient is increased from an inflow portion 9 to the high temperature end portion 10, its temperature rises and the quantity of radiation is increased whereby the refrigeration efficiency of the very low temperature refrigerator is improved.