Lighting device and luminaire including the same

A lighting device (10) includes a voltage converter (2) for generating a predetermined DC voltage, a detector (4) for obtaining a detection voltage corresponding to a predetermined DC voltage applied across a light source (20), a controller (3) for controlling the voltage converter (2) so that a current flowing through the light source (20) is constant, and a determination unit (5) for determining whether the detection voltage is a preset first reference voltage or higher. The first reference voltage is set higher by a specified voltage than the detection voltage, and is set to vary more slowly than the detection voltage. The controller (3) stops an operation of the voltage converter (2) when the detection voltage is determined to be the first reference voltage or higher through the determination unit (5).