PURPOSE:To enable a test piece to be processed with high accuracy without making any shifts in slit parts by enabling a test piece secured by a clamping device to be fixed rotatably by a rotating device at a predetermined rotating angle. CONSTITUTION:A cylindrical rock test piece 28 is fixed on a clamping device 24 in a state wherein the axis is coincided with the axis of a rotating shaft of the rotating device 23. Next, the rotating device 23 is rotated in order that the symmetrical surfaces of clamping materials 29, 29 are allowed to be 45 with respect to a support shaft 27, and then fixed by a securing pin 33. The rotating blade of a machine tool is shifted to the surface of a table in parallel within the surface that is vertical to the test piece 28, and a part of the slit parts is formed therein. Then, the securing pin 33 is dislodged therefrom and the rotating device 23 is turned at 90 deg., and the symmetrical surfaces are permitted to be -45 deg. with respect to the surface that is vertical to the support shaft 27, and thereafter the rotating device 23 is fixed again by the securing pin 33. When the rotating blade of the machine tool is shifted within the same surface as preceding case, an unmolded part of the slit part is formed within the same surface as the precedingly formed slit without making any shifts therein.
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