A source driver includes a ladder circuit for outputting multilevel gradation voltages by resistance voltage division, a first decoder for selecting one gradation voltage corresponding to the inputted image data to output the selected gradation voltage, an external power supply for supplying multilevel pre-charging voltages, a second decoder for selecting one pre-charging voltage corresponding to the image data, an operational amplifier for outputting the driving voltage corresponding to the inputted gradation voltage to the source electrode, a pre-charging switch interconnected between the operational amplifier and second decoder, and a controller for controlling the pre-charging switch. The connection between the first decoder and operational amplifier is always kept during the whole sampling period including a pre-charging period, and the controller controls the pre-charging switch to be turned on during the pre-charging period and turned off after the pre-charging period has expired.