PURPOSE: To prevent damage to a buried pipe by transmitting a current signal to a buried conductive pipe for a transmission line, and by detecting the current signal from the buried pipe through a member which advances underground when a civil working machine is driven.

CONSTITUTION: A current signal I is transmitted to a buried conductive pipe 1 from a position on the ground surface which is different from the advanced position of a member 3 driven underground by a civil working machine 6, and a magnetic field M is effected around a buried pipe 1 for a transmission line. Meanwhile, when the member 3 advancing underground approaches the buried pipe 1, the magnetic field M is detected at the front end of the member 3. Further, the operation of the civil working machine 6 comes to a stop in response to the detected signal, and accordingly, the driving operation of the member 3 is stopped. Further, the buried conductive pipe 1 can be detected when it is hidden underground. With this arrangement, the approach of the member 3 to the buried pipe 1 may be detected with a high degree of accuracy so as to stop the advance of the member 3. It is possible to prevent damage to the buried pipe 3.