A gamma voltage generation unit is discussed which includes: a voltage booster to boost a first maximum reference voltage into at least one second maximum reference voltage; a mode selector configured to select one of the maximum reference voltage and the at least one second maximum reference voltage as a selected maximum reference voltage; and a plurality of gamma voltage adjusters. The selected maximum reference voltage selected by the mode selector is provided as a 255th gray-scale gamma voltage. A first gamma voltage adjuster among the gamma voltage adjusters can generate the 255th gray-scale gamma voltage and another gray-scale gamma voltage based on the selected maximum reference voltage. The remaining gamma voltage adjusters are connected to one another in a cascade.