PURPOSE:To support an object with accurate centering and carry out accurate machining by inserting a piezoelectric ceramic inside a hollow cylindrical object, applying a voltage to the piezoelectric ceramic and outwardly expanding same and pressing the inner wall face of the object. CONSTITUTION:A silver layer, etc., for an electrode is formed on the most inside of a piezoelectric ceramic body 11 while also forming a silver layer, etc., for functioning as the other electrode on the most outside, and titanium nitride layers, etc. for covering these layers are formed on top thereof respectively. When a switch 13 is turned on, the piezoelectric ceramic body 11 is uniformly expanded outward forming roundness and closely brought into contact with a workpiece 7 to fix same. Hence, the center point of the workpiece 7 agrees with the center point of the piezoelectric ceramic body 11 without causing the shift of center, enabling accurate machining of a workpiece 7 at the time of rotating a motor 9. Not only a workpiece but any optional object can be coaxially supported as far as the object is a hollow cylindrical object.