PURPOSE: To prevent the occurrence of air-unstable vibration by a simple method in which in the manufacturing process of a cable covered with polyethylene, a mixture with polyethylene chips and sand is projected from the surface of the cable in such a way as to form roughened surface.

CONSTITUTION: In the manufacturing process 1 of a diagonal suspended bridge cable covered width polyethylene layer 2, the cable element is mixed with molten polyethylene chips, fibers, and sand to form the polyethylene layer 2 on the cable element in such a way as to form a roughened surface with projected sand mixture 3. Since the apparent Reynolds' number becomes more than limit Reynolds' number, no Karman vortex occurs in the back flow, permitting the occurrence of air-unstable vibration to be prevented simply.