An LNG carrier having an LNG loading and unloading system includes a submerged turret loading (STL) system for introducing and discharging a natural gas; a liquefaction plant for liquefying the natural gas introduced through the submerged turret loading system into a cryogenic liquefied natural gas; at least one self-supporting storage tank installed in the LNG carrier for storing the liquefied natural gas, the self-supporting storage tank arranged in such a manner that the liquefied natural gas is loaded to and unloaded from the LNG carrier through the self-supporting storage tank; and at least one membrane type storage tank arranged in a neighboring relationship with the self-supporting storage tank, the membrane type storage tank kept in fluid communication with the self-supporting storage tank. The LNG carrier further includes a regasification plant for regasifying the liquefied natural gas stored in the self-supporting storage tank.