In a rehabilitation of an existing steel structure, column bases are often treated as reinforced elements. This paper proposes a new reinforcement of the column base. In the reinforcement method, existing anchor bolts of the column base resist an axial force and a shearing resistant plate resists a shearing force. Experimental study on the new reinforcement of the column base was carried out. The following conclusions were obtained from the experimental results: 1) The shearing resistant plate resisted the shearing force of a brace, and anchor bolts resisted the tensile force; 2) Tensile stress of the anchor bolt reached an yield stress; 3) The existing anchor bolts can be designed as a tension member, and this reinforcement of the column base by the shearing resistant plate is effective.