PURPOSE: To decrease the number of voltage levels of a signal voltage and decrease the number of analog switches required to drive signal electrodes by generating opposite-phase AC rectangular waves as signal voltages for half- tone writing and dark writing.

CONSTITUTION: While a light signal voltage is varied from Vd1 to Vd2, the half-tone signal voltage is varied from Vd3 to Vd4. Then the dark signal voltage is varied from Vd4 to Vd3. Namely, the dark signal voltage is opposite in phase from the half-tone signal voltage. Further, a scanning voltage Vc is so set that Vc1=(Vs2+Vn)×5/6 and Vc2=0 for a selection and that Vc3=(Vs2+Vn)/2 and Vc4=Vn for a nonselection signal. Thus, the signal voltage Vd can be set to four levels Vd1-Vd4. The number of the necessary analog switches can, therefore, be decreased to four and when IC where many analog switches are integrated are used, the number of the ICs in use can be decreased.