A display device in which the influence of a parasitic capacitance or a wiring capacitance is suppressed without lowering OFF-current of a switching transistor or increasing the capacitance of a capacitor, and a driving method thereof using area gray scale display in particular. The display device of the invention comprises a plurality of sub pixels each including a driving transistor whose gate potential is fixed, and area gray scale display is achieved. Specifically, each of the sub pixels comprises, in addition to the driving transistor, a switching transistor, a current controlling transistor connected in series with the driving transistor, and a light emitting element.