PURPOSE: To shorten the drilling time by optimizing the time (delay time) in drilling a printed circuit board placed on a work table movable in X and Y directions using a drilling tool.

CONSTITUTION: A work table 14 movable along X and Y directions is provided through the rotation of a motor of two lead screws 26, 28 along X-axis and Y-axis is provided, and a plurality of printed circuit boards are placed on the table 14. Each printed circuit board 30 is drilled by a drilling tool 13 attached to a spindle 18 movable in Z-axis. A positioning scale 34 including a reading head 38 is provided on a drilling machine 10 to determine the correct position of the table 14. During the drilling, the optimum dwell time is automatically selected from a computer memory device based on the tool diameter and the drilling position, the table is moved to the drilling position, and the drilling is achieved after the elapse of the dwell time.