PURPOSE: To reduce the used amount of powder of an electrostatically charged water-absorptive swelling material and to prevent the powder from being dispersed in air by sticking the powder on an optical fiber core stack body.

CONSTITUTION: The powder 1 of the water-absorptive swelling material supplied from a hopper 2 to a conveyer is carried to under a spacer 7 by a belt 4. A conductor 6 fitted to the internal surface of a cover 9 made of an insulating seal is applied with a voltage from a device 5 as well as the belt 4. When the powder 1 is a dielectric with a high resistance value, polarizing operation is caused by an electric field between the spacer 7 and belt 4 to generate positive charges on the powder 1 and negative charges on the side of the belt 4. Then when negative charges under the powder 1 are neutralized by the potential of the belt 4, electric force which attracts the powder 1 to the side of the spacer 7 is generated and the powder 1 sticks on the grooved spacer 7 where optical fibers are stacked.