PURPOSE: To provide the final centering method in a machine dedicated for drilling work which comprises a workpiece mounting fixture and a drill head used for a purpose of drilling a predetermined number of holes on a pitch circle of a workpiece in a condition of positioning.

CONSTITUTION: A master workpiece 20 with a circumferential groove 21 is mounted to a supporting shaft 5 of a workpiece mounting fixture. A test indicator is mounted to one of the spindles of a drill head. The master workpiece 20 is provided with a mounting hole 22 for fitting the supporting shaft 5 and the concentrical circumferential groove 21 formed by arranging groove surfaces 24, 23. After center height of the mounting fixture agrees with center height of the spindle of the drill head, a measuring piece of the test indicator is rotated, and by bringing this measuring piece into contact with internal/external wall surfaces 23, 24 of the circumferential groove 21, a position thereof is measured. Thereafter, centering in a horizontal direction of the centers of mounting fixture and the drill head is performed based on a measured value.