Technology is discussed of detecting structures buried in the ground by use of a forward-looking sensor mounted on the drill head for the avoidance of collision with such structures during application of the flowmole method in urban districts. In this detection system, pulsating radio signals are emitted from a transmission antenna and the received signals are converted into low-frequency signals in a sampling circuit for eventual display on a B-scope. Since the drill head for flowmole technology is as small as approximately 50-60mm in diameter, experiment is conducted to know the detectability of a very small antenna directed at a buried pipe. The basic phase of the experiment using the very small antenna includes a soil-filled tank test and field test. It is then found that the very small antenna is capable of detecting the steel pipe buried 50cm away from the antenna with the antenna directed at the said pipe. In a test wherein a very small antenna is allowed to rotate on the drill propelling shaft, the design simulating a revolving drill head, it is learned that the detecting system under study will identify the direction in which a buried structure exists. 1 ref., 9 figs.