A clamping member for reliably inserting a protrusion portion thereof into a mounting hole of a cutting insert so as to engage the protrusion portion with an inner peripheral surface of the cutting insert and strongly clamp the cutting insert on a tool holder. The clamping member includes a body having a top surface engageable with a head of a clamping bolt, a bottom surface facing the tool holder and a bolt hole for insertion of the clamping bolt, and a protrusion portion protruding from the bottom surface and being engageable with a mounting hole formed in the cutting insert. The protrusion portion has an inclined surface facing toward a rotational direction about a center axis of the clamping bolt, the inclined surface is inclined so that the protrusion portion is gradually tapered from a base side thereof proximate the bottom surface toward an end side thereof distal from the bottom surface.