<p>An apparatus to re-liquefy boil-off gas is disclosed. According to an embodiment of the present invention, the apparatus to re-liquefy boil-off gas comprises: a first heat exchanger passed primarily by boil-off gas discharged from a storage tank for liquefied natural gas; a first compressor to compress the boil-off gas having passed primarily the first heat exchanger; and a refrigerant supply device to supply refrigerant to the first heat exchanger. The compressed boil-off gas having passed the first compressor secondarily passes the first heat exchanger in the process of moving to the storage tank for liquefied natural gas.</p>
