To moderate the restriction which accrues in the boil-off gas treatment by utilizing the boil-off gas produced at the time of filling the liquefied natural gas from a tanker in order to raise the pressure in the tanker or to reduce the quantity of diffusion into the atmospheric air. ! The boil-off gas discharged from the upper part of the first storage tank 1 is supplied through the pipe 21 for the first tanker and a part of the first liquefied natural gas filling pipe 2 from a part of the forth piping 18 to the bottom side of the tanker TL, and the pressure in the tanker TL is increased while reducing the pressure in the first storage tank 1. Thereafter, the supply of the boil-off gas from the first storage tank 1 to the tanker TL is stopped and the pressure in the tanker TL is raised up to the set pressure by a pressurizer 29 for the tanker, which the liquefied natural gas in the tanker TL is supplied into the first storage tank 1 through the first liquefied natural gas filling pipe 2. ! (C)2007,JPO&INPIT