PURPOSE: To smoothly and securely spread a film bag, by releasing clamping state by a clamp in a state that the opening of a film bag is spread to the intermediate position or in a state that the outer-side film bag than a suction device is opened half and preventing the outside film bag from contacting other materials due to its swinging with wield.

CONSTITUTION: The side edge A near the opening 5a is clamped by a clamping device 30. A film bag is transferred downward by the lowering movement of the clamping device 30 and the side B thereof is positioned to face to an opening device 20. Sucking devices 23 are closely positioned to each other and after suction of the side B they are separated from each other. The opening of film bag 5 is gradually spread. Since the side edge A is clamped by the clamping device 30, the opening forms hexagonal. In the intermediate stage of the spreading process, he clamping state of the side edge A is released and the opening 5a is gradually spread to form quadrilateral.