the memory cell in the unselected state the voltage lower than the polarization reversal voltage v 1 described above applied between the electrodes of the capacitor element c for information storage in the memory cell in the unselected state can be e g one half of the saturation voltage v 0 by this construction at each of the information writing operation and the information reading operation since only the voltage lower than the polarization reversal voltage v 1 is applied between the electrodes of the capacitor element c for information storage in the memory cell in the unselected state it is possible to prevent the reversal of the polarization direction of the ferroelectric material layer 5 and thus the destruction of the information written in the capacitor element c for information storage as the result electrical reliability on the operation of the memory device can be improved further a same voltage is applied to the common plate electrode serving as one of the electrodes i e the upper electrode of the capacitor elements c for information storage in the memory cells in the selected state and those in the unselected state in the memory device described above by this construction it is possible to form the upper electrode of the capacitor element c for information storage of a memory cell in one body with the upper electrodes of the capacitor elements c.