A liquefied gas treatment system, comprising: a liquefied gas supply line connected from a liquefied gas storing tank to a source of demand; a heat exchanger provided on the liquefied gas supply line between the source of demand and the liquefied gas storing tank and configured to exchange heat between liquefied gas, supplied from the liquefied gas storing tank, and heat transfer medium; a medium heater configured to heat the heat transfer medium and to supply the heated heat transfer medium to the heat exchanger; a medium pump configured to supply the heat transfer medium to the medium heater; a medium circulation line connecting the medium pump, the medium heater and the heat exchanger to circulate the heat transfer medium; a branch line branched at an upstream point of the medium heater on the medium circulation line to be joined at a downstream point of the medium heater on the medium circulation line to cause at least some of the heat transfer medium to be branched from the medium circulation line to bypass the medium heater; a liquefied gas temperature sensor provided on the liquefied gas supply line and configured to measure a temperature of the liquefied gas, and a controller including a target temperature calculator for calculating a target temperature of the heat transfer medium by using the measured temperature of the liquefied gas, and configured to change a flow rate of the heat transfer medium flowing into the medium heater on the basis of the target temperature of the heat transfer medium, wherein target calories of the heat transfer medium are calculated considering the target temperature calculated by the target temperature calculator, a flow rate of the heat transfer medium detected by a medium flow rate sensor, and a flow rate of the liquefied gas detected by a liquefied gas flow rate sensor, and wherein the controller changes the flow rate of the heat transfer medium flowing into the medium heater by controlling driving of the medium pump or the flow rate of the heat transfer medium on the basis of the target calories of the heat transfer medium. a liquefied gas supply line connected from a liquefied gas storing tank to a source of demand; a heat exchanger provided on the liquefied gas supply line between the source of demand and the liquefied gas storing tank and configured to exchange heat between liquefied gas, supplied from the liquefied gas storing tank, and heat transfer medium; a medium heater configured to heat the heat transfer medium and to supply the heated heat transfer medium to the heat exchanger; a medium pump configured to supply the heat transfer medium to the medium heater; a medium circulation line connecting the medium pump, the medium heater and the heat exchanger to circulate the heat transfer medium; a branch line branched at an upstream point of the medium heater on the medium circulation line to be joined at a downstream point of the medium heater on the medium circulation line to cause at least some of the heat transfer medium to be branched from the medium circulation line to bypass the medium heater; a liquefied gas temperature sensor provided on the liquefied gas supply line and configured to measure a temperature of the liquefied gas, and a controller including a target temperature calculator for calculating a target temperature of the heat transfer medium by using the measured temperature of the liquefied gas, and configured to change a flow rate of the heat transfer medium flowing into the medium heater on the basis of the target temperature of the heat transfer medium, wherein target calories of the heat transfer medium are calculated considering the target temperature calculated by the target temperature calculator, a flow rate of the heat transfer medium detected by a medium flow rate sensor, and a flow rate of the liquefied gas detected by a liquefied gas flow rate sensor, and wherein the controller changes the flow rate of the heat transfer medium flowing into the medium heater by controlling driving of the medium pump or the flow rate of the heat transfer medium on the basis of the target calories of the heat transfer medium.