A vessel including a storage tank for storing liquefied gas is disclosed. The vessel comprises: a heat exchanger for heat-exchanging compressed boil-off gas (hereinafter, referred to as "first fluid") by using, as a refrigerant, the boil-off gas discharged from the storage tank, so as to cool the same; a main compression part for compressing a part of the boil-off gas discharged from the storage tank; a rest compression part provided in parallel to the main compression part so as to compress the other part of the boil-off gas discharged from the storage tank; and a decompression device for expanding the first fluid having been cooled by exchanging heat with the boil-off gas, which is discharged from the storage tank, in the heat exchanger, wherein the first fluid is: a flow in which the boil-off gas compressed by the main compression part and the boil-off gas compressed by the rest compression part join; or the boil-off gas compressed by the main compression part.