Abstract: The Fuel supply system reduces fuel quantity initially supplied and ineffective residual quantity of fuel. A throat in the shape of a passage is provided at a bottom portion of a sub-tank that supplies fuel from the fuel tank to the interior of the sub-tank by a jet pump. The throat has a suction port communicating with the exterior of the sub-tank and a supply port communicating with the interior of the sub-tank. The throat is inclined with respect to a bottom surface of the tank so that the height of the throat increases gradually from the suction port toward the supply port. The sub-tank has a check valve for opening and closing the supply port. This check valve prevents the fuel in the sub-tank from flowing out to the exterior of the sub-tank through the throat and becomes substantially vertical during valve closing.