To provide a driver for a semiconductor light emitting element in which high class feeling is enhanced visually when an outer light system device or an illuminator in a vehicle employing the semiconductor light emitting element as a light source is unlighted.

The driver (10) for a semiconductor light emitting element comprises a control section (20) and a drive section (30). Upon receiving a designation signal (S10) for unlighting the semiconductor light emitting elements (LEDS1, LEDS2), the control section (20) provides the drive section (30) with a control signal (S20) for shortening the time of applying a voltage to the semiconductor light emitting elements and lengthening the time of not applying the voltage gradually every specified period while repeating application and non-application of the voltage to the semiconductor light emitting elements alternately for a specified time interval thus applying no voltage to the semiconductor light emitting elements at the end of the specified time interval.