The reliability of an EL element is enhanced while the increase of the
electric power consumption is suppressed. It becomes possible that in a
SES drive, the reverse bias is applied to the EL element driven at a
constant electric current. Moreover, the application of the reverse bias
is performed by varying only the counter electrode, and thus withstand
voltage of TFT and the increase of the electric power consumption due to
the increase of voltage of the gate signal line drive circuit, which
becomes a problem when changing greatly the electric current supplying
line, can be suppressed. Furthermore, the reduction of the electric power
consumption can also be achieved while the enhancement of the reliability
is secured by making the reverse bias smaller than the forward bias.
Moreover, the increase of the number of electric sources can be also
suppressed by making the potential be in common with the potential of the
electric source of the source signal line drive circuit or the gate
signal line drive circuit, at the time when the reverse bias is applied.