PURPOSE: To transmit the data of a sensor in a banked earth without interrupting the cruise of a ship and without being attracted in the banked earth, by providing a protecting tube concentrically around the outer periphery of a metal rod through a sound shielding material.

CONSTITUTION: The protecting tube 3 is provided concentrically around the outer periphery of the metal rod 1 through a sound shielding layer 2. At the lower end 1a of the metal rod 1, an ultrasonic oscillator, i.e., a transmitter 4 to generate an ultrasonic wave is provided, and at the upper end 1b of the metal rod 1, an ultrasonic lens 7 is provided through a matching layer 6. When the transmitter 4 is driven, the ultrasonic wave is generated, and the ultrasonic wave is radiated from the ultrasonic lens 7 through the metal rod 1 and the matching layer 6. At that time, since when the ultrasonic wave passing through the metal rod 1 progresses toward the outer peripheral surface of the rod 1, it is reflected by the sound shielding layer 2, the leakage of the ultrasonic wave to the banked earth is prevented. Then, all the ultrasonic wave generated at the transmitter 4 is radiated from the upper end 1b of the metal rod 1.