PURPOSE: To increase the adhesion efficiency of a granular material, by a method wherein a cylinder is raised along the inner cavity surface of the hollow body of a suspension insulator from below and the granular material in the cylinder is scattered in a horizontal direction by centrifugal force while extruded in a definite ratio by a piston.

CONSTITUTION: After a cylinder 8 is filled with a granular material such as sand, a first cylinder 3 is operated to raise a base 2 and the cylinder 8 on the base 2 is inserted in the inner cavity part 51 of the hollow body 50 of a suspension insulator. At this time, the hood 16 around the cylinder 8 is preliminarily raised by a third cylinder 17. Next, when a piston 12 is raised with respect to the cylinder 8 by a second cylinder 14 while the cylinder 8 and the piston 12 are simultaneously rotated at a high speed by a motor 10, the granular material is extruded from the open end of the cylinder 8 to be scattered in the horizontal direction by centrifugal force and effectively adhered to the inner cavity part 51 preliminarily coated with glaze and the falling portion of the granular material is recovered by the hood 16.