Abstract: An automatic wrench comprises a high-torque, a low-torque, and a locking device. The wrench control system includes a torque detector and a rotation angle detector, in response to whose signals passing through an AND gate a control unit delivers a command to end the thread tighening by the rotation actuator of the high-torque device in screwing a pipe string together or to end the initial loosening of the thread with the aid of the same actuator in screwing it apart. The control unit incorporates a unit for monitoring the duration of the command execution, which stops operation of the high-torque device if no signal comes from said AND gate during the time alloted to accomplish the tightening or the initial loosening of the thread.