PURPOSE: To detect the laid and buried positions readily by arranging an armored cable having an ultrasonic-wave-leakage transmitting path along the entire length of a subaqueous cable, and detecting the leaking ultrasonic waves over the water.

CONSTITUTION: An armored cable with ultrasonic-wave-leakage transmission path 6 is arranged along the entire length of a subaqueous cable 1. The armored cable 6 is separated from the main body of the cable 1 and connected to an ultrasonic oscillator 5 at the land part. In this way, even if the cable 1 is in the operating state, the ultrasonic waves transmitted from the oscillator 5 are propagated through the transmission path of the armored cable 6 and then become leaking ultrasonic waves through a leaking path. Therefore, the buried position of the cable 1 is detected by receiving the leaking ultrasonic waves with an ultrasonic receiver 4 equipped on a survey ship 3 over the water. In details, the leaking ultrasonic waves 2 are received with the receiver 4 on the survey ship 3, and the position of the maximum transmission is confirmed and recorded, or the position is indicated directly with a buoy. Thus, the laid/buried positions of the cable 1 can be detected accurately and readily.