To provide a reinforcing method of a concrete pile applied to civil engineering and a building structure, which can economically and effectively cope with a horizontal forces during an earthquake.

A bending moment on a pie head part generated by the horizontal force during the earthquake concentrates in proximity to the pile head part. In order to cope with the concentrated bending moment generated by the horizontal force, the portion of the concrete pile head part for the concentration of the bending moment is reinforced by winding steel pipes around it. Thus, the steel pipe pile reinforcing method of the concrete pile head part has a cross-sectional structure which enables the pile head part to cope with the horizontal force most economically and efficiently during the earthquake.