A circuitry and a driving method thereof in which a reverse voltage is applied to a light emitting element to control the degradation thereof and improve reliability for a display device comprising a pixel circuit.A first power source line is connected to a signal line through a switching transistor and erasing transistor, and a current controlling transistor and driving transistor are connected in series between the first power source line and a light emitting element. An analog switch including first and second transistors whose gate electrodes are connected to the first and second power source lines respectively is provided. Further, a bias transistor whose gate electrode is connected to a third power source line, one of source and drain electrodes thereof is connected to the first power source line, and the other is connected to an output terminal of the analog switch and a scan line is provided.