PURPOSE: To enhance productivity, to reduce a cost, to make a titled device small-sized, and to realize its long life, by reducing resistance of water by forming its case in an elliptical cone, preventing a cavitation by raising internal pressure, and utilizing the vibration of 3 directions by a ring-like vibrator.

CONSTITUTION: A bottom surface of a fish detector is shaped in an ellipse. A vibrator 5 is fixed to a shaft 6 with an E-ring 9. Oil 10 is put into an inside case 2, and internal pressure is raised by a rubber stopper 11 and a cap 12, by which a cavitation is prevented. A radiation surface of the inside case 2 is formed in a long ellipse in the advancing direction of a ship, by which the front and rear directional angles are narrowed, influence by a screw sound, etc. is reduced, and the searching range is expanded by widening the left and right directional angles, and also resistance of water is reduced. Also, wide band frequency can be selected by forming the vibrator 5 like a ring. That is to say, by utilizing the vibration of 3 directions, frequency can be selected on site and radio interference can be prevented.