By controlling an excessive rise in the temperature of the material gas that is introduced into the liquefaction unit following the compression by a compressor, the temperature of the material gas may be adjusted to the temperature level at the introduction point of the liquefaction unit. A system (1) for the liquefaction of natural gas, comprises a first expander (3) for expanding natural gas under pressure as material gas; a first cooling unit (10, 11, 12) for cooling the material gas; a distillation unit (15) for reducing or eliminating a heavy component in the material gas by distilling the material gas cooled by the first cooler; a first compressor (4) for receiving a top fraction of the material gas from which the heavy component was reduced or eliminated by the distillation unit; and a liquefaction unit (21) for liquefying a gas phase component separated from the compressed material gas compressed by the first compressor by exchanging heat with a refrigerant.