PURPOSE: To obtain a method for recovering ethylene from a soft gas under low temperature in which high recovery rate is achieved by using refrigerant in supercooled state.

CONSTITUTION: Intermediate temperature mixed refrigerant vapor 1 is compressed through a compressor 101 and cooled down to the ambient temperature through contact with air or water by means of a heat exchanger 103. Condensed mixed refrigerant 3 is supercooled through a mixed refrigerant supercooler 107 to produce a supercooled mixed refrigerant 5. A part 11 of the supercooled mixed refrigerant 5 is flushed across an expansion valve 109 and passed through the mixed refrigerant supercooler 107 in order to provide additional freezing. A second part 15 of the supercooled mixed refrigerant 5 is flushed across an expansion valve 111 and fed to the overhead condenser 113 of a deethanizer where the mixed refrigerant is produced and vaporized partially. A third part 19 of the supercooled mixed refrigerant 5 is flushed across an expansion valve 115 and a supply material gas 23 is fed as a flow being cooled and partially condensed under a low pressure. It is conducted in a normal temperature supply material condensing region 117 to produce a soft gas flow 25 and a liquid condensate 27.