Disclosed herein is arrangement of a fuel gas tank in a fuel gas supply system that supplies liquefied natural gas to an engine. In accordance with one aspect of the invention, a fuel gas supply system of a ship includes an engine generating driving force using fuel gas; and a fuel gas tank storing the fuel gas to be supplied to the engine, wherein the engine is disposed in an engine room placed at the stern of the ship and the fuel gas tank is disposed above the engine room.