A stereoscopic image display comprising: - a display panel including data lines, gate lines crossing the data lines, and a plurality of pixels, each of which includes a main display unit and an auxiliary display unit, the main display unit and the auxiliary display unit being respectively connected to the data line through a first switch and a second switch, both switches being controlled by the gate line; - a data driving circuit configured to supply a data voltage of a 2D image to the data lines in a 2D mode and supply a data voltage of a 3D image to the data lines in a 3D mode; and - a gate driving circuit configured to sequentially supply a scan pulse, which swings between a gate low voltage and a gate high voltage, to the gate lines in the 2D mode and the 3D mode; characterized in that - the display panel is divided into a first screen block and a second screen block and includes a first discharge control line (CONL1) and a second discharge control line (CONL2), and - the auxiliary display units of the first screen block are connected to a common line through a discharging switch which is controlled by the first discharge control line (CONL1) and the auxiliary display units of the second screen block are connected to a common line through a discharging switch which is controlled by the second discharge control line (CONL2) wherein the stereoscopic image display further comprises: - a control voltage generator configured to generate in the 3D mode a first discharge control voltage of a first alternating current waveform and a second discharge control voltage of a second AC waveform, of which a phase is later than a phase of the first AC waveform by a half frame period, and to generate in the 2D mode the first discharge control voltage and the second discharge control voltage at a same level as the gate low voltage and - a control voltage delay means configured to delay the first and the second discharge control voltages to be respectively supplied to the first and the discharge control lines (CONL1, CONL2). - a display panel including data lines, gate lines crossing the data lines, and a plurality of pixels, each of which includes a main display unit and an auxiliary display unit, the main display unit and the auxiliary display unit being respectively connected to the data line through a first switch and a second switch, both switches being controlled by the gate line; - a data driving circuit configured to supply a data voltage of a 2D image to the data lines in a 2D mode and supply a data voltage of a 3D image to the data lines in a 3D mode; and - a gate driving circuit configured to sequentially supply a scan pulse, which swings between a gate low voltage and a gate high voltage, to the gate lines in the 2D mode and the 3D mode; - the display panel is divided into a first screen block and a second screen block and includes a first discharge control line (CONL1) and a second discharge control line (CONL2), and - the auxiliary display units of the first screen block are connected to a common line through a discharging switch which is controlled by the first discharge control line (CONL1) and - a control voltage generator configured to generate in the 3D mode a first discharge control voltage of a first alternating current waveform and a second discharge control voltage of a second AC waveform, of which a phase is later than a phase of the first AC waveform by a half frame period, and to generate in the 2D mode the first discharge control voltage and the second discharge control voltage at a same level as the gate low voltage and - a control voltage delay means configured to delay the first and the second discharge control voltages to be respectively supplied to the first and the discharge control lines (CONL1, CONL2).