PURPOSE: To transmit pressure to a frame beam, and to uniformly distribute clamp force to grip a work and fixing force of the movable jaw in relation to the frame beam by pressing a closing device to a spacer belonging to the closing device.

CONSTITUTION: For example, a closing device 6 composed of a heart wheel is arranged in a main body 2 installed on a frame beam 1. The movable jaw 4 closes by being pressed to the fixed jaw 3 by this closing device 6. At the same time, a clamp is fastened to the frame beam 1, so that the closing device 6 rotatably journalled to a shaft 7 arranged in the movable jaw 4 is pressed to the frame beam 1 to thereby generate clamp force F between the jaws.