Abstract: The present invention provides a cryogenic refrigerating system for achieving ultra low temperature by sequentially obtaining low temperature through repetition of expansion and evaporation of a mixed-refrigerant in multiple stages. The refrigerating system includes a heat exchanger and a compressor between a final evaporator and a compressor. The heat exchanger causes evaporated refrigerant vapor in a suction tube for the compressor to be heated and to be drawn into the compressor, and causes the refrigerant condensed by a condenser to be supercooled. The refrigerating system includes a plurality of expansion/suction apparatuses connected with one another between the gas/liquid separator and the final evaporator.