The present invention relates to a liquid crystal display device and, More specifically, the invention relates to an in-plane field type liquid crystal display device. 
In general, an in-plane field type liquid crystal display device is provided with a pixel electrode and a counter electrode spaced apart from the pixel electrode in each pixel area on a liquid-crystal-side surface of one of transparent substrates which are opposed to each other via a liquid crystal, and is arranged to control the optical transmittance of the liquid crystal by means of an electric field which occurs between the pixel electrode and the counter electrode. 
A liquid crystal display device of an active matrix type which adopts the in-plane field mode includes, on a liquid-crystal-side surface of one of its transparent substrates, scanning signal lines extended in the x direction and juxtaposed in the y direction, counter signal lines extended in the x direction and juxtaposed in the y direction, and video signal lines extended in the y direction and juxtaposed in the x direction, and each area surrounded by scanning and counter signal lines adjacent to each other and a pair of video signal lines adjacent to each other is formed as a pixel area. 
In each pixel area, a thin-film transistor driven by the supply of a scanning signal from the scanning signal line and a pixel electrode to which a video signal is supplied from one of the video signal lines via the thin-film transistor are formed. 
In this case, since a voltage corresponding to the video signal on the basis of the counter electrode is applied to the pixel electrode, a reference voltage is applied to the counter electrode via the counter signal line. 
In such a liquid crystal display device, since its structure is such that its thin-film transistors are easily damaged by static electricity, it is indispensable to take measures against static electricity. 
As an attempt at taking measures against static electricity, there is an art in which a protection element common line is formed to surround a display area made of an assembly of pixels, and scanning signal lines and video signal lines are connected to the protection element common line via non-linear elements at the intersections of the scanning and video signal lines and the protection element common line. 
For example, the art of taking measures against static electricity in a liquid crystal display device which differs in structure from the in-plane field mode is described in Japanese Patent Laid-Open No.  90428/1997.