To provide a construction method of a strut, by which preferable rust-preventive measures can be taken.

A multi-layer sheet 10 is bonded onto the part of the strut near the ground surface by one turn. The multi-layer sheet 10 comprises a butyl-based adhesive material 11 as the first layer, a resin-reinforcing film 12 as the second layer, an aluminum foil 13 as the third layer, and a fluororesin film 14 as the fourth layer and as a surface layer. The butyl-based adhesive material is covered with the aluminum foil. The aluminum foil reflects the sunlight and exerts an effect of completely blocking ultraviolet rays, in particular. Consequently, the butyl-based adhesive material is not deteriorated by irradiation of the ultraviolet rays. However, the aluminum foil corrodes due to the salt spread on a road surface in a cold region or due to other exhaust gas components. That is why the aluminum foil is protected with the fluororesin film. Consequently, secular change of the butyl-based adhesive material can be prevented and corrosion of the aluminum foil can also be prevented, so that the part of the strut near the ground surface can be prevented from rusting over a long period of time.