To quickly carry out center hole machining and end-surface machining to a work by providing such drill advancing/retreating device as to transfer a rod in the axial direction of a main spindle so that a center drill emerges from or recedes into a shaft center part of a milling cutter in the axial direction.

At the completion of end-surface machining by means of a milling cutter 16, working oil is supplied to a working oil passage 38 of the advancing side of a drill advancing/retreating device 35 to advance a piston 37, and projects a center drill 28 toward right side of the milling cutter 16 via a rod 25a on the right part. In this condition, an x-axis servo-motor of each head-moving device is rotated in the e.g. normal direction so as to rotate a ball-bearing screw in the normal direction, so that each head-supporting table, or each main spindle head 10, proceeds, thereby a center-hole at the shaft center part on both end surfaces of the work is drilled by the center drill 28 of the main spindle head 10.