PURPOSE: To make an apparatus small in size, to expand the scope of investigation and also to enable the investigation of a buried substance with no dead angle, by providing a plurality of transmission antennas and by arranging them zigzag so that they overlap each other.

CONSTITUTION: A plurality of transmission antennas 12a to 12c are provided and arranged zigzag so that they overlap each other, while a reception antenna 14 being one or more and less than the number of the transmission antennas 12a to 12c is so disposed as to face an array of the transmission antennas. A trigger circuit 32 generates a pulse of a prescribed width at a fixed period and delivers it to transmitters 30a to 30c and a receiver 34. Receiving the pulse, each of the transmitters 30a to 30c generates a transmission wave of a prescribed frequency and they emit the wave simultaneously from the corresponding transmission antennas 12a to 12c into the ground 36. The wave propagates through the ground 36, and when a buried substance 38 exists in the ground 36, a reflected wave therefrom is received by the reception antenna 14. Then, an averager 40 averages a signal inputted from the receiver 34 and removes a noise component therefrom, and the signal is subjected to a signal processing 42 and displayed in a display device 46.