PURPOSE: To secure a free main spindle distance and permit the speedy and easy adjustment by installing a means which mounts each main spindle in the Z-axis direction onto a plurality of sliders and guides each slider in the Y-axis direction and a means for reciprocative movement.

CONSTITUTION: When a printed circuitboard having a size of A×C is to be worked, a main spindle 2 is retreated rightward by a distance Y2 and set in repose, and the whole surface of the printed circuitboard is worked by shifting a main spindle 1 in reciprocation within the distance Y1=A. IN this case, a replacement drill within a range of D1 is to be used. Then, the surface 1 of the printed circuitboard having a board size of 2P2 (main spindle distance is P2) is drilled, and the surface 2 having a board size P2 is drilled, and further, the surface 4 having a board size of P2/2 is drilled, and also the surface 6 having a board size of P2/3 is drilled. In this case, a replacement drill for a drill plate 21l is used for the main spindle 1, and a replacement drill for a drill plate 21r is used for the main spindle 2.