To restrain the unneccessary movement of a drilling head and shorten a working hour by controlling so as to switch the moving direction of a drilling head to an opposite direction when a detected load torque is below the set drilling judge torque, after the start of drilling by a drill.

A drilling head 7 is moved to the left direction approaching to the work with a quick feed speed by the operation of a hydraulic cylinder 25 under the rotation state of a drill 15 by a drive motor. When the hit of a drill 15 tip to the work is detected from the load torque detected by a load torque detector 51, a speed selector valve 47 is switched and the moving speed of a drilling head 7 is switched to a cutting feed speed and the drilling to the work is carried out. Then, during this drilling, when the detected load torque is below the pre-set drilling judge torque, it is judged that the drill 15 penetrates the work and the direction selector valve 35 is controlled so as to switch the moving direction of the drilling head 7 to the opposite direction.