To produce a green case of good quality by dividing the cylindrical rubber band arranged to the almost entire surface of a drum along the surface crossing the axis of the drum in the lateral direction of the drum to form a large number of round slices to disperse gaps generated by shrinkage.

Three cylindrical rubber bands 7, 8, 8 divided in a round slice shape in the lateral direction of a drum along a surface wherein the rubber bands cross each other at a right angle with respect to the axis of the drum are attached to the surface of a drum segment 5. The center rubber band 7 widely coveres the center part of the drum and narrow side rubber bands 8, 8 cover both end parts of the drum. The width of the side rubber band 8 is set to about 20mm. The parts applied to the cut ports of the center rubber band 7 and the side rubber band 8 are obliquely cut off in a truncated chevron shape from the surfaces of the rubber bands becoming the surface of the drum and the cut-off angle θ based on the surfaces of the rubber bands is set to about 45°.