A processing device is provided with a circuit connected to a first conductive portion and a second conductive portion. An AC voltage source produces an AC waveform voltage obtained by adding a bias voltage to an AC voltage for capacitance measurement. The AC waveform voltage is applied between the first conductive portion and the second conductive portion through the measurement probes. The moment the AC waveform voltage is applied to the circuit with a switch closed, an inrush current flows through the circuit based on a potential difference of the bias voltage. This inrush current causes dielectric breakdown in the conductive resin, thereby securing the continuity of the conductive resin. With the continuity of the conductive resin secured, a capacitance of the piezoelectric body is measured by the AC waveform voltage, and it is determined whether or not the piezoelectric body is normal.