A horizontal driving circuit includes: a shift register for performing shift operation in synchronism with a first clock signal HCK and sequentially outputting a shift pulse from each of shift stages thereof; a first switch group for extracting a second clock signal DCK in response to the shift pulse sequentially outputted from the shift register; and a second switch group for sequentially sampling an input video signal in response to the second clock signal DCK extracted by each switch of the first switch group, and supplying the sampled video signal to each of signal lines. An external clock generating circuit is disposed external to a panel to externally supply the horizontal driving circuit with the first clock signal HCK, and an internal clock generating circuit is disposed within the panel to internally supply the horizontal driving circuit with the second clock signal DCK.