A semiconductor device which can supply an accurate current without being affected by the variation of transistors for supplying currents to EL pixels even when the signal current is small is provided. A video signal voltage is inputted to each signal line dot-sequentially. This operation corresponds to a precharge operation to a video signal current which is inputted subsequently. After the input of the video signal voltage, a video signal current is inputted to each signal line. Accordingly, an effect of variation of a transistor in each pixel can be reduced. In addition, since a video signal voltage is inputted prior to the input of a video signal current, signal writing speed can be increased even when the signal current is small. Further, as a video signal voltage is inputted dot-sequentially, simple configuration can be realized.