A liquid crystal display device includes a thin film transistor arranged at crossings of gate lines and data lines; a pixel electrode connected to each thin film transistor; a common electrode arranged on a second substrate; a layer of liquid crystal material provided between the first and second substrates; a protrusion arranged on the common electrode for controlling an orientation of the liquid crystal molecules within the layer of liquid crystal material; and a common voltage generator applying an AC common voltage to the common electrode, wherein a polarity of the common voltage is inverted every predetermined period.