PURPOSE: To provide a centering device capable of perforating a discharge hole in a nozzle without fail.

CONSTITUTION: A nozzle 7 is placed on an X-Y table 6 so that the hole 8 may be directed downward. A picture of the hole 8 is taken from the underside of the table 6 by using a camera 10 according to the polarization lighting method and the taken image signal is treated through an image processor 11 to determine the position of the apex of the conical hole 8. A drill 4 is set above the table 6 and the table 6 is subjected to controlled drive so that the coordinate position of the drill 4 may coincide with the detected coordinate position of the apex of the conical shape.