An apparatus for reliquefaction of boil-off gas generated in a liquefied gas storage tank provided to a vessel, comprising: a compressor compressing BOG discharged from the storage tank; a heat exchanger performing heat exchange of the BOG compressed by the compressor with the BOG discharged from the storage tank, the BOG having passed through the heat exchanger being divided into at least two flows comprising a first flow and a second flow; a first expansion unit expanding the first flow; a first intermediate cooler cooling the second flow remaining after division into the at least two flows using the first flow expanded by the first expansion unit as a refrigerant; a receiver receiving the second flow having passed through the first intermediate cooler, a level control line regulating a level of the receiver by discharging a fluid from the receiver, the fluid discharged from the receiver being divided into at least two flows comprising a third flow and a fourth flow, wherein at least some of the fluid discharged through the level control line is returned to the liquefied gas storage tank, a second expansion unit disposed on the level control line and expanding the third flow; and a second intermediate cooler cooling the fourth flow remaining after division into the at least two flows using the third flow expanded by the second expansion unit as a refrigerant, a third expansion unit disposed on the level control line and expanding the fluid returned to the liquefied gas storage tank along the level control line, wherein the fourth flow having passed through the second intermediate cooler is returned to the liquefied gas storage tank and the third flow having passed through the second intermediate cooler is supplied to the compressor, wherein pressure downstream of the compressor is controlled by the receiver. a compressor compressing BOG discharged from the storage tank; a heat exchanger performing heat exchange of the BOG compressed by the compressor with the BOG discharged from the storage tank, the BOG having passed through the heat exchanger being divided into at least two flows comprising a first flow and a second flow; a first expansion unit expanding the first flow; a first intermediate cooler cooling the second flow remaining after division into the at least two flows using the first flow expanded by the first expansion unit as a refrigerant; a receiver receiving the second flow having passed through the first intermediate cooler, a level control line regulating a level of the receiver by discharging a fluid from the receiver, the fluid discharged from the receiver being divided into at least two flows comprising a third flow and a fourth flow, wherein at least some of the fluid discharged through the level control line is returned to the liquefied gas storage tank, a second expansion unit disposed on the level control line and expanding the third flow; and a second intermediate cooler cooling the fourth flow remaining after division into the at least two flows using the third flow expanded by the second expansion unit as a refrigerant, a third expansion unit disposed on the level control line and expanding the fluid returned to the liquefied gas storage tank along the level control line, wherein the fourth flow having passed through the second intermediate cooler is returned to the liquefied gas storage tank and the third flow having passed through the second intermediate cooler is supplied to the compressor, wherein pressure downstream of the compressor is controlled by the receiver.