PURPOSE: To maintain the writing rate of a positive polarity voltage equal to the writing rate of a negative polarity voltage and to prevent flicker and seizure by prolonging the time for turning a thin-film transistor(TFT) at the time of writing the positive polarity voltage at an on state.

CONSTITUTION: A clock CLK 1 synchronized with the period of horizontal scanning is taken out of a control circuit 1 and is inputted to a frequency bi- dividing circuit 2. The period of the output signal a of this frequency bi-dividing circuit 2 is 2H if the period of the clock signal CLK 1 is assumed to be 1H (one horizontal scanning period). The output of a first monostable circuit 3 is then a signal b and the output of a second monostable circuit 3 is a signal c. If the respective signals b, c are inputted to a logic circuit 5 which is a NOR circuit, the output thereof is a waveform CLK 2. This CLK 2 is used as the output voltage changeover signal of a horizontal driver 14 to make the time for impressing the positive polarity signal voltage of a drain wiring longer than the time for impressing the negative polarity signal voltage.