To solidly hold a retaining wall on a slope surface by simple and easy work of inserting and driving a hollow pipe pile into a drilling hole drilled in advance in the ground from the slope surface of cutting or banking.

In a drilling step, a drilling hole 16 of a prescribed depth is formed in a horizontal direction or an inclined direction by a compaction type excavator 14 in the ground of cutting or banking through a hole 13 opened on a retaining wall 12. A hollow pipe pile 19 provided with a branching piece 20 on a distal end is pushed into the hole 13 and the drilling hole 16, the hollow pipe pile 19 pushed into the drilling hole 16 is driven further into the ground using driving force of the compaction type excavator 14, the branching piece 20 is expanded in the ground, and the branching piece 20 expanded in the ground is made to strengthen resistance force in the inserting direction of the hollow pipe pile 19 and a withdrawing direction opposite to the inserting direction to a soil pressure respectively.