To determine the three-dimensional buried status of an underground buried article in the vicinity of a drill head intuitively and easily.

Transmission and reception antennae 16 are incorporated into a drill head, electromagnetic waves are radiated into soil from the antennae 16, and reflected waves are received and a buried article is investigated by a radar system. The travel (x) of a jacking body, the reflection time (t) of reflected waves by the buried article and an angle θ in the periphery of the axis of the drill head are detected respectively. The buried status of the buried article is detected by combining the first data of coordinates (x, t) and the second data of coordinates (θ, t). The existence of the buried article in a front in front of the jacking direction when the second data is placed in symmetry at 180° when the first data is indicated in an inclined straight line and the oblique existence of the slender buried article when the second data is extended in one direction of the radial direction are decided.