PURPOSE: To change and set the material to be worked in an optional arrangement type easily and quickly, by providing a selection mechanism which can optionally take the state fixed to a movable support body and the state freely rotatably to the movable support, on a rotation support body.

CONSTITUTION: A rotation support body 3 is separated from a movable support body 2 and becomes in the state of freely rotatable because the lower end tip 26 of a rod 15 presses the plate like body 12 of a freely rotating mechanism 25 with its projecting from the lower end of a projection part 10, as a selection mechanism 6 pushes down a ball 16 at its operative piece 17, when the rotation support body 3 is in a freely rotatable state. Then, when the operative piece 17 is moved in the opposite direction and the ball 16 is sunk into a hole 19, the movable rod 15 loses a support force, the rotation support body 3 is descended with its gravity, the upper flat part 23 of the movable support body 3 and its lower flat part 24 are brought into contact and the rotation support body 3 thus becomes in a fixed state to the movable support body 2.