A driving method that does not allow a change in temperature of the surroundings to change the luminance of a light emitting element of a pixel is provided for a display device with less uneven display, higher gradation, and reduced power consumption. A time ratio gradation driving method is applied to a pixel that is structured to have a current mirror circuit and use a current drive method. The bit number of digital video signals to be sampled by a source signal line driving circuit is reduced with the use of a switching signal, thereby saving the power consumption when high gradation display is not necessary.