A tool holder has an apparatus for clamping a cutting insert thereto. The tool holder has a cutting insert pocket and a mounting bore; a clamp lever including a clamp portion and a lever portion placed in the mounting bore; and a fixing screw. The fixing screw is fastened through a hole which extends downwardly from a side wall of the tool holder to the mounting bore. One end of the fixing screw further includes a pressure-applying surface substantially perpendicular to the rotational axis of the fixing screw, and the side surface of the lever portion of the clamp lever has an inclined surface which makes contact with the pressure-applying surface of the fixing screw. According to the clamping apparatus, the cutting insert can be firmly clamped to the tool holder.