PURPOSE: To eliminate the necessity for mounting an inclination bearing measuring device in a digging pipe and to always perform monitoring from the ground, by radially providing a large number of antennae around the digging pipe under tension from a digging platform or digging rig performing directional drilling to the ground or the bottom of water and providing an analyser capable of analyzing the difference of the receiving intensity of the reflected wave from the digging pipe of an electromagnetic wave.

CONSTITUTION: A large number of antennae 3 are radially provided around a digging pipe 2 under tension from a digging rig 1 so as to extend along the bottom B of water. When the antennae 3 are radially provided around the digging pipe 2 under tension, for example, at a 45°-interval, the receiving intensity of the reflected wave Y from the digging pipe 2 at each antenna 3 when the digging pipe 2 is vertical is different from that when the digging pipe 2 is inclined and the difference in the receiving intensity is analyzed by the analyser provided on the digging rig 1 to detect the inclination bearing of the digging pipe 2.