PURPOSE: To promote simplification and facilitation of a manual operation by reducing the torque to be required in rotating an actuating and tensioning rod as much as possible in a clamp element provided with a rapid feeder combined with a force amplifier.

CONSTITUTION: A tightening pin 13 is supported on a second clamp member 11 with a minimum interval (a) from a feed sleeve shaft A. An actuating and tensioning rod 10 is passed through a central aperture of a first clamp member or a lateral aperture opposite to two diameter directions of a first clamp member 5. The lateral aperture is sufficiently large in the circumferential direction of the feed sleeve 2, and the actuating and tensioning rod 10 is rotatable in a restrictive manner to the feed sleeve 2 so as to be sufficient to rotate the second clamp member 11 with respect to the first clamp member 5.