The invention has a monitoring portion which detects change of ambient temperature and degradation with time, provided with a plurality of monitoring pixels and a monitoring line. Each of the plurality of monitoring pixels has a light emitting element for monitoring, a constant current source, a switch, and a detecting circuit, and one electrode of the light emitting element for monitoring is connected to the monitoring line through the switch. The detecting circuit controls on and off of the switch, and specifically in the case where both electrodes of the light emitting element for monitoring are short-circuited, the switch is turned off. The invention having the aforementioned configuration generates no potential change of the power supply line of the pixel portion when both electrodes of a light emitting element for monitoring are short-circuited.