PURPOSE: To enable three-dimensional positions of hydrophones under sea to be detected by providing three transmitters which are at equal angles and in parallel for a suspension cable for transmitting signal and by allowing the hydrophones to receive the signal.

CONSTITUTION: Three rear arms 8 which are thrown into sea are expanded in horizontal direction and at mutually equal angles. After expansion, a signal processing part 5 transmits signal from three transmitters 9 at a certain interval. Then, hydrophones 4 receive this signal and send it to the processing part 5 by a suspension cable 2. Then, the processing part 5 detects arrival times of reception signal, detects signal arrival times after obtaining transmission time information of the arm 8, and obtains arm identification information from the transmitter 9. Also, it identifies position of each arm based on orientation information from a compass 7 and sends it to a transmission part 6 along with signal arrival time and arm identification information as transmission signal. Then, the transmission part 6 transmits this transmission signal by electric wave. Processing device sides such as ship and aircraft which received this electric wave can detects three-dimensional positions of the hydrophones 4 from these pieces of information.