Abstract: A piezoelectric device comprises a ferroelectric ceramic plate as polarized, and electrodes formed on two main surfaces thereof, respectively, intersecting the polarization axis direction. The electrodes are connected to each other by means of an external resistance having a predetermined resistance value. The resistance value is selected to be smaller than the inherent resistance value of the ferroelectric ceramic plate between the two main surfaces. The positive and negative electric charges are stored on the two electrodes due to the pyroelectric effect responsive to a change of the temperature of the ferroelectric ceramic plate. The potential difference caused by the electric charges thus stored is rapidly decreased through the external resistance.