The present invention relates to a boil-off gas treatment system for treating boil-off gas discharged from a storage tank in which liquefied gas is stored. According to the present invention, the boil-off treatment system for treating boil-off gas discharged from a storage tank in which liquefied gas is stored comprises a compressor for compressing boil-off gas generated in a storage tank; a heat exchanger for cooling the boil-off gas compressed by the compressor; and an expansion unit for decreasing the pressure of the boil-off gas cooled by the heat exchanger. The heat exchanger heat-exchanges the boil-off gas compressed by the compressor and the boil-off gas discharged from the storage tank and supplied to the compressor.
