A liquid crystal display device includes a display unit having matrix type pixels defined by gate and data lines crossing with each other, a data driver to supply a data voltage to be supplied to the data lines via output lines, the output lines being less in number than the data lines, a plurality of demultiplexers, each including a plurality of switching devices having a gate terminal, source terminal and a drain terminal, wherein the gate terminals are supplied with a plurality of control signals, the source terminals are commonly connected to the corresponding output line, and the drain terminals are individually connected to one side of the data lines, respectively, a data line check unit activated to supply a test data voltage to the other side of the data lines when the data driver is inactive, a plurality of signal input lines individually connected to the gate terminals, respectively, an input terminal supplied with a cutoff signal to be inputted to the signal input lines to turn off the switching devices, and a switching unit electrically connecting/disconnecting the input terminal to/from the signal input lines according to an external control signal.