A ship having a liquefied petroleum gas storage tank for storing liquefied petroleum gas with a boiling point of higher than -110 °C at 1 atm, the ship comprising: a first heat exchanger and a second heat exchanger; a multistage compressor comprising a plurality of compression cylinders (21, 22) configured to compress boil-off gas discharged from the storage tank to the saturated liquid pressure corresponding to the temperature of the fluid discharged from the second heat exchanger; the second heat exchanger configured to cool the fluid compressed by the multistage compressor and liquefying at least a portion of the fluid compressed by the multistage compressor by heat exchanging between the compressed fluid and seawater, the first heat exchanger configured to supercool the liquefied portion of the fluid liquefied by the second heat exchanger by subjecting the fluid to heat exchange with the boil-off gas discharged from the storage tank to the multistage compressor; a first decompressor configured to expand one (hereinafter referred to as "flow a1") of two flows branching off of the fluid supercooled by the first heat exchanger (hereinafter referred to as "flow a"); a third heat exchanger configured to cool the other flow (hereinafter referred to as "flow a2") of the two flows by subjecting the flow a2 to heat exchange with the flow a1 expanded by the first decompressor to be used as a refrigerant; and a second decompressor configured to expand the flow a2 cooled by the third heat exchanger, wherein the fluid expanded by the first decompressor and having been used as a refrigerant in the third heat exchanger is supplied to the multistage compressor, and at least a portion of the fluid having passed through the second heat exchanger becomes a saturated liquid. a first heat exchanger and a second heat exchanger; a multistage compressor comprising a plurality of compression cylinders (21, 22) configured to compress boil-off gas discharged from the storage tank to the saturated liquid pressure corresponding to the temperature of the fluid discharged from the second heat exchanger; the second heat exchanger configured to cool the fluid compressed by the multistage compressor and liquefying at least a portion of the fluid compressed by the multistage compressor by heat exchanging between the compressed fluid and seawater, the first heat exchanger configured to supercool the liquefied portion of the fluid liquefied by the second heat exchanger by subjecting the fluid to heat exchange with the boil-off gas discharged from the storage tank to the multistage compressor; a first decompressor configured to expand one (hereinafter referred to as "flow a1") of two flows branching off of the fluid supercooled by the first heat exchanger (hereinafter referred to as "flow a"); a third heat exchanger configured to cool the other flow (hereinafter referred to as "flow a2") of the two flows by subjecting the flow a2 to heat exchange with the flow a1 expanded by the first decompressor to be used as a refrigerant; and a second decompressor configured to expand the flow a2 cooled by the third heat exchanger, wherein the fluid expanded by the first decompressor and having been used as a refrigerant in the third heat exchanger is supplied to the multistage compressor, and at least a portion of the fluid having passed through the second heat exchanger becomes a saturated liquid.