PURPOSE: To position a reference aperture for a multilayer substrate without providing a dowel part for the top layer of the substrate by precisely and quickly searching for a reference mark for the second layer and below.

CONSTITUTION: A drill device 3 is supported in such a way that it can be moved in the X and Y axis directions. A workpiece transfer mechanism for supporting a multilayer substrate (B) on the drill device 3 is provided. A sensor 2 which moves in the X and Y axis directions above a reference mark C in the multilayer substrate (B) supported by the workpiece transfer mechanism 4 while issuing searching signals (eddy currents) to detect the intensity of the reflection of the searching signals is also provided. An image processing part 5 which displays the reference mark (C) on a monitor 5a based on the scanning signals from the sensor 2 and a control part which calculates the center of the reference mark C' displayed on the monitor and moves the drill device 3 to the center are also provided.