Abstract: An ultrasonic vibration and a voltage are applied to a submerged marine structure to exert thereon vibrational and electric energies, thereby effecting deterioration prevention of the structure. An ultrasonic vibration unit comprises an ultrasonic vibrator made from a piezoelectric ceramic plate with an electrode on each side thereof; power supply wires connected to the respective electrodes; a support member for fixedly supporting the ultrasonic vibrator and transmitting the ultrasonic vibration to the structure; and a resin coat for protecting the ultrasonic vibrator against seawater. The ultrasonic vibration unit is used for preventing deterioration of the submerged marine structure.