There has been a problem that power consumption is increased if a potential of a signal line changes every time a video signal is applied to a driving transistor from the signal line, since the parasitic capacitance of the signal line stores and releases electric charges. In a configuration of a display portion provided with a gate signal line for selecting an input of a video signal to a pixel and a source signal line for inputting a video signal to the pixel, a switch is connected in series with the source signal line, the switch being controlled to be in on state when the pixel is not selected by the gate signal line, and in off state when the pixel is selected by the gate signal line. Accordingly, the parasitic capacitance of the source signal line which stores and releases electric charges affects only pixels between an output side of a source driver up to and including the pixel selected to be written with a video signal. Consequently, power consumed by the charging and discharging of the source signal line can be reduced, and thus low power consumption can be achieved.