An ultrasonic probe system is disclosed, which is designed to allow connection of a DC power supply capable of applying a voltage higher than the coercive electric field of each of a plurality of piezoelectric layers thereto, and includes a polarization turn over circuit means for, when the DC power supply is driven, turning over the polarity of the DC power supply so as to direct electric fields of every two adjacent layers constituting the piezoelectric layers in substantially opposite directions or electric fields of all the layers in the same direction. When the polarization turn over circuit means turns over the polarity of a voltage to be applied to direct electric fields of every two adjacent layers of the piezoelectric layers in substantially opposite directions or electric fields of all the layers in the same direction, the polarization turn over circuit means performs control to apply the voltage during a blanking time of an operating time of the system, thereby performing conversion of a resonance frequency, and selectively generating ultrasonic waves having a plurality of different frequencies.