Disclosed is a common voltage regulating circuit of a liquid crystal display device which can be adjusted by software, comprising: a pulse signal generating means for outputting a pulse width modulation signal in response to up/down signal for adjusting a common voltage; a smoothing means for smoothing a pulse width modulation signal to a direct current level provided from the pulse signal generating means; and an amplifying means for amplifying the signal smoothed by the smoothing means to a predetermined level and then outputting a common voltage signal Accordingly, since a common voltage can be adjusted by software, by means of a surplus pulse width modulation signal generated in an integrated board without installing a separate hardware, the common voltage can be easily adjusted. Further, since a variable resistor has not been used, not only manufacturing cost but also possibility of breakage can be reduced.