To provide a clamp device not requiring provision of any separate clamp part or to be moved temporarily in the case there is no place to clamp a work to be machined within the configuration of the intended component when the work is going to be cut in tracing the configuration of the component.

A crank base 3 is fixed to the part to be cut away of a work to be machined 10. The oversurface of the crank base 3 is inclined toward the inside of the work 10, and one end of a clamp bar 2 is attached by a pin bolt 4 to that surface perpendicularly thereto, and the work 10 is pressed by the tip extended striding the cutting part. A torque is given oppositely to the cutter 8 advancing direction, and the clamp bar 2 is installed abutting to a stopper pin 13. The clamp bar 2 rotates being pressed by the cutter 8 at the time of cutting process, and when the cutter 8 is separated, restitution is made to the initial position by the torque and the work 10 is pressed.