The invention addresses the problem of providing a centering guide that is easy to operate and can detect deviation of the position of a tool that is to be inserted into a bone with high sensitivity, and a surgical tool for treatment of bone fractures comprising said centering guide. The problem is solved by using a polygonal marker, particularly double rings the respective internal diameters of which differ but the centers of which are the same, as the marker, and using a rod that passes through a substantially perpendicular plane above the center of the double rings and extends along the guide arm as the indicator.
