To provide a ship including a re-liquefying device capable of liquefying ethylene in addition to BOG of LPG, with no use of a refrigerating cycle that uses a refrigerant such as freon.

A ship includes a gas compressor 15 for compressing petroleum gas, an LPG condenser 17 being cooled by a water temperature, a swelling tank 13 in which LPG is decompressed and stored, an ethylene condenser 11 which condenses and liquefies ethylene gas, and a flow path switching means which switches the flow paths of the LPG and the liquefied ethylene so that, in a case in which LPG is stored in a cargo tank 3, the LPG that is condensed and liquefied by the LPG condenser 17 is introduced into the cargo tank 3, and in a case liquefied ethylene is stored in the cargo tank 3, the liquefied ethylene that has been condensed and liquefied by the ethylene condenser 11 is introduced into the cargo tank 3 while the LPG that has been condensed and liquefied by the LPG condenser 17 is introduced not into the cargo tank 3 but into the swelling tank 13.