To reuse a driving anchor itself even if the surface of an existing driving anchor material is rusted and corroded, because it has sufficient plate thickness and strength.

Cleaning is carefully performed on the surface of the existing driving anchor material, and an welding auxiliary material is welded and fixed to a base material surface of the anchor material so that the existing anchor material and the welding auxiliary material can be firmly welded and fixed. In the remarkably corroded driving anchor material, a skeleton is chipped off, and a new anchor material is installed.