PURPOSE: To provide a method for manufacturing continuously a buffer bag from a tubular raw fabric wherein a thermally welded part is restricted to a minimum necessary limit, its quality is stabilized, and a defect is little.

CONSTITUTION: A pushing member 14 provided to a base end side of a tubular raw fabric 11 wherein an intermediate part and the base end part are blocked up, is operated to transfer gas on the base end side, and a small bag is formed this die from the intermediate part of the tubular raw fabric 11. A gas injecting nozzle 19 is inserted into the small bag to its middle to release pushing on the base end side of the tubular raw fabric 11. Besides, blocking up of the middle part of the tubular raw fabric 11 is released to inject gas from the gas injecting nozzle 19, and the blocked up tubular raw fabric 11 at the top part is further inflated. Then, under a state wherein the gas injecting nozzle 19 is extracted, a heat-sealed part is formed on both sides of the tubular raw fabric 11 which is opened with the gas injecting nozzle 19.