PURPOSE: To prevent breakage of a boom caused by erroneous operation in drilling, and to prevent breakage of a reel table when drilling is not operated.

CONSTITUTION: A pressure switch 28 that makes contact by operation of circuit pressure is provided to a rod-side circuit 17 of an oil-hydraulic cylinder 8, and a solenoid-controlled selector valve 29 that is electrified on contact-making of the pressure switch 28 and breaks a discharge-side circuit of an operating oil-hydraulic pump 25 with the solenoid 29a excited is provided to the discharge- side circuit of the oil-hydraulic pump 25. Therefore, a directional control valve 23 that controls the revolution of an oil-hydraulic motor 21 of a rotative driving device 7 cannot be operated when a rope 11 is stretched tight.