Data (gray scale levels of source driver output) of two lines are compared between an actually charged line and a pre-charged line for which actual charging and pre-charging are carried out, respectively, during the same horizontal period. Based on the result of comparison, a pre-charged period of the pre-charged line is adjusted by adjusting a pulse width of a gate driver output. In this way, the pre-charge period is reduced and thereby overcharge is avoided in pixels which are likely to be overcharged by the pre-charging.