PURPOSE: To reduce weight, to reduce drive torque, to avoid toxity, and to perform safe processing of a biomaterial by forming a grinding grain layer on the outer polishing surface of a base metal formed such that a low friction material is mixed in a TiMg alloy.

CONSTITUTION: A base metal 1 is formed of a TiMg alloy or an alloy prepared such that a low friction material, such as MoS, is mixed in the TiMg alloy. A grinding grain layer 2 is formed on the outer peripheral polishing surface of the base metal 1 by using grinding grains, such as diamond, CBN, and TiC, through a metal bond serving as a binder. Grinding liquid flow holes 3 and 6 opened to the outer peripheral grinding surface are formed in the base metal 1 and communicated to a pump 7 through a grinding liquid feed passage 5. The grinding liquid flow holes 3 and 6 are formed radially in the direction of a radius or at a specified inclination angle from the center of the base metal 1.