In a liquid crystal display device of the present invention, a source line is formed of a gate metal and a gate line is formed of a source metal for reduction of the number of masks, whereby deterioration of a liquid crystal on the gate line is prevented. During a period in which the liquid crystal display is not used, an inverse voltage for preventing deterioration of the liquid crystal is applied to it. In addition, when the gate line is scanned, a width of a start pulse inputted in a shift register for driving a gate line is increased to approximately ten times as large as an ordinary width to improve a duty ratio in an inverted period of the gate line.