Pulse voltages V1 and V2 are applied to the first upper gate electrode and the second upper gate electrode, respectively, for a period T1 which is shorter than a period necessary to invert all the polarizations included in the ferroelectric film, while voltages Vs, Vd, and V3 are applied to the source electrode, the drain electrode, and the lower gate electrode film, respectively, so as to increase the values of the widths WRH1 and WRH2 and so as to decrease the value of the width WRL. The pulse voltages V1 and V2 have a smaller voltage than a voltage necessary to invert all the polarizations included in the ferroelectric film. The voltage Vs, the voltage Vd, the voltage V3, the pulse voltage V1, and the pulse voltage V2 satisfy the following relationship: Vs, Vd, V3