PURPOSE: To enhance the working ability, by providing such an arrangement that a movable shaft and a slide dog are moved integrally with a working head to turn on a limit switch, and when the working head is advanced to complete fabrication, the slide dog is made to abut against the stopper.

CONSTITUTION: Upon starting of fabrication, a slide dog 19 turns on, at its rear pressing surface 20, an initial position detecting limit switch 31, nd serrations 13 on a movable shaft 6 are meshed with teeth 26 on a pressing member 25 in the slide dog 19 so that a working head 3 is fast-fed.When a slide dog 19 passes through a limit switch 32, and drills 14... are positioned just before a position where they make into contact with a workpiece, a feed speed change-over limit switch 33 is turned on so that the feed speed of the working head 3 is changed over into a low feed speed mode.Simultaneously, the slide dog 19 abuts against an adjusting bolt on a stationary stopper 36 so that it is inhibited from advancing, and then the working head is moved backward at a fast-feed speed. With the repetitions of the above-mentioned motion to complete the drilling of the workpiece.