PURPOSE: To obtain an output with a small error without being affected by a noise magnetic field by processing the outputs of a couple of magnetic sensors by a comparator and generating an indication output only when a received output signal is zero or smallest.

CONSTITUTION: A couple of magnetic sensor coils L1 and L2 which are equal in characteristic value are arranged coaxially at an interval (d). When those coils L1 and L2 move on the buried conductor 1, induced voltages are detected at respective positions of the conductor 1. The difference between both detection signals is obtained and further inverted by a comparator to generate the output only when the reception output is zero or smallest. This output is amplified and displayed on an indication meter, etc. Consequently, the conductor 1 is easily and accurately detected.