PURPOSE: To reduce an amount of flush gas generated in unloading to carry out easily the unloading operation for a short time by making the internal pressure in an LNG tank on land at least equivalent to that of a tank on a coastal LNG tanker.

CONSTITUTION: An LNG tank 11 on land is made of a pressurized tank having at least storing pressure in a tank 3 on a coastal LNG tanker 2. Under the condition that the internal pressure in the pressurized tank 11 is made at least equivalent to that in the tank 3 of said tanker 2 is unloaded LNG in the tank 3 on said tanker 2 to the LNG tank 11 on land under a reduced amount of flush gas generated.