PURPOSE: To efficiently fill a developer into a bag while preventing the developer from flying up by a method wherein the developer is fed into a bag from above with the bottom closed and simultaneously sucked from the surroundings of the bag by a suction device.

CONSTITUTION: A suction device 50 is equipped with a cylindrical suction drum 52 having a number of vent holes around the inside circumference and located below a guide 2, and supersonic sealing members 42 are located below the suction drum 52. A sheet material 11 formed into a tubular shape is lowered along a guide 2, and the bottom of the sheet material 11 is sealed by the supersonic sealing members 42 so that a bag 10 is formed. After that, a specified amount of developer is fed into the bag 10 through a feed pipe 3, and simultaneously the bag 10 into which the developer is fed is drawn by the suction device 50 from the surroundings of the bag 10. The sheet material of the bag 10 is made of a laminated sheet of which non-woven fabric of very fine polypropylene fiber is laminated on non-woven fabric of ordinary polypropylene fiber by supersonic welding.