PURPOSE: To prevent the drilling of pipelines and the like due to a boring machine by detecting the existence or non-existence of an undergound magnetic buried material such as a gas pipe, a cable or the like by the variation in the rotation torque produced in the drill.

CONSTITUTION: To a part of the rod of a boring machine, for example, a mounting part of a drill 4 there is mounted a permanent magnet 5, and a torque senser 6 is provided around the periphery of the rod 3. When a magnetic buried material M such as a gas pipe, a water feed pipe or a cable exists in the drilling direction of the drill 4, and the drill 4 reaches the proximity of the buried material M, the attractive force of the permanent magnet 5 acts on the buried material M to vary the rotation torque of the rod 3. The senser 6 detects the variation of the rotation torque, and the detection signal is measured by a torque meter 9. The result of the measurement is determined by a comparator 10 to control the boring machine, and to carry out the transmission of the alarm, the feed stopping or extraction of the drill.