PURPOSE: To drill a positioning hole at an accurate position from the position of a photo-conductive wave passage buriedly provided without influence resulting from the external form and material of an optical part and the dispersion of the external form.

CONSTITUTION: A drilling device for machining the a positioning hole of an optical part is provided with a XY stage 2 which can move slightly with an optical part mounted on it and a turning arm 4 serving as a mechanism to alternately shift a microscope 6 with 2 reticle and a boring head 5 at the same positin on the XY stage 2, and a positioning hole is machined by the boring head 5 at a position which is fixed from a photo-conductive wave passage on the basis of the photo-conductive wave passage of the optical part through the reticle.