PURPOSE: To obtain the accurate detection information of an embedded article, by detecting a reflected wave of every receiving channel to hold the same by a sample holding circuit and removing a DC component from the signal held to said circuit.

CONSTITUTION: Radio waves sent out from antennae 1A, 1B are reflected from ground surface and an underground embedded article to be received by antennae 2A, 3A and 2B, 3B and respectively detected by the detectors 7AW7D of channels CH1WCH4. The detection signals outputted from the detectors 7AW7D are respectively inputted to sample holding circuits 8AW8D and held at the detection signal level of a receiving time band of a previous cycle during the non-receiving time band of the reflected waves. The signals outputted from the circuits 8AW8D are inputted to filters 9AW9D to remove DC components thereof to obtain signals of only AC components. That is, ground surface reflected wave components are removed by the filters 9AW9D. The outputs of the filters 9AW9D are inputted to judge devices 10AW10D from which underground embedded article presence signals are in turn outputted.