In case the size of the transistor is enlarged, power consumption of the transistor is increased. Thus, the present invention provides a display device capable of preventing a current from flowing to a display element in signal writing operation without varying potentials of power source lines for supplying a current to the display element per row. In setting a gate-source voltage of a transistor by applying a predetermined current to the transistor, a potential of a gate terminal of the transistor is adjusted so as to prevent a current from flowing to a load connected to a source terminal of the transistor. Therefore, a potential of a wire connected to the gate terminal of the transistor is differentiated from a potential of a wire connected to a drain terminal of the transistor.