PURPOSE: To absorb vibration at the time of high speed rotation of a raw rod material by pressingly inserting the raw rod material at a suppoting material with use of a holder under proper pressure by movement of a cylinder by the action of the supporting material and a buffer material of a supporting box in co-operation with the holder.

CONSTITUTION: A raw rod material (A) put into a suppoting material is moved to the chuck position of the machine body 1 by a holder of a cylinder 10 in a supporting box 6. Next to it, the holder is reprogressed and returned to one extremity of the supporting material 17. Then, the holder is sent down by the movement of a cylinder 11, the raw rod material (A) is pressed and inserted at the supporting material under proper pressure. In this case, said supporting box 6 is vertically moved through a nut 9 in mesh with the screw part of a guide post 7 in order to bring the raw material (A) into a coincidence with the axial line of the machine body 1. In this condition, the raw rod material is chucked, rotated at high speed for machining, vibration of the raw rod material at the time of rotating is absorbed by the action of the supporting material 17 and a buffer material 16 of the supporting box 6 in co-operation with the holder.