PURPOSE: To prevent the quantity of imbalance of an eccentric member owing to the dislocation of a center hole from being scattered by pressing the end surface in the eccentric direction of the eccentric member with a movable supporting member after the eccentric member of a work has been adjusted about an axial center, and thereby boring a center hole on the axial end surface of the work while the eccentric member is being held at an eccentric center.

CONSTITUTION: When the eccentric member 2 of a workpiece 1 which is forged so as to be formed, is held at its suitable point near by its axial section 4 by a self- alignment type jig 21, one end plane surface 11 of the eccentric member 2 is accepted by the upper end surface of a stationary support member 22 first. Concurrently, one end of a pressing member 27 is advanced so that the eccentric member 2 is uniformly pressed by the tip end section of a pair of rotating support members 25 to the direction normal to the eccentric one while the eccentric member 2 is adjusted about an axial center O over the stationary support member 22. Then, the other end of a pressing member 26 is advanced so that the front end surface 12 in the eccentric direction of the eccentric member 2 is pressed by a movable support member 23. Thus, a center hole 8 is bored on the axial end surface 6 of the workpiece while the eccentric member 2 is being held at the axial center O.