It is a problem to provide a light-emitting device capable of obtaining a constant brightness without being affected by deterioration in an organic light-emitting layer or temperature change, and of making desired color display. The lowering in OLED brightness due to deterioration is reduced by causing the OLED to emit light while keeping constant the current flowing through the OLED instead of causing the OLED to emit light while keeping constant the OLED drive voltage. Namely, OLED brightness is controlled not by voltage but by current thereby preventing against the change in OLED brightness due to deterioration of OLED. Specifically, the drain current Id of a transistor for supplying a current to the OLED is controlled in a signal line drive circuit thereby keeping constant the drain current Id without relying upon the value of a load resistance.