To surely detect the position of an underground buried pipe with a relatively simple work.

Electromagnetic field 62, 64, 66 generated by a corrosion protective current fed by full-wave rectification of an AC power 38 without smoothing is detected by a detector 70 from the ground to search the position of an underground buried pipe 32 to be electrically protected. When the corrosion protective current flows through the underground buried pipe 32, the electromagnetic field is generated around from the underground buried pipe 32, so that the position of the underground buried pipe 32 can be surveyed without needing to provide a transmitter or the like by detecting this electromagnetic field. In case of a power cable being buried adjacently, the sizes of both magnetic field of power frequency and double frequency are simultaneously detected, and a position of detecting only the magnetic field of double frequency can be identified as the position of the buried pipe.