To provide a method of providing horizontal recess parts in plural steps in the periphery of a concrete columnar body such as a pier, for enhancing operational efficiency in providing, using a wall cutter, the plurality of horizontal recess parts vertically in the outer surface of the columnar body for the purpose of carrying out construction work for reinforcing the columnar body to make it earthquake resistant, while omitting the need for the work of replacing a rail for guiding the wall cutter.

A hanging scaffold 2 is placed along the outer periphery of a columnar body 1 and a wall cutter mounting frame 4 is slidably placed at the inner peripheral end of the hanging scaffold 2 via an adjusting jack 5. A rail 6 is attached to the wall cutter mounting frame 4 and the horizontal position of the hanging scaffold 2 is fixed to the columnar body 1 by a support jack 11. After a wall cutter is displaced around the columnar body 1 along the rail 6 to provide a horizontal recess part in the surface of the columnar body 1, the height position of the hanging scaffold 2 is appropriately moved up and down to repeat the above processes.