In a lighting device, a voltage detector outputs a detection voltage with a magnitude corresponding to a magnitude of a DC voltage outputted from a power supply circuit, a state determiner makes determination of whether a light source is in a turned-on state or in a turned-off state, a power controller is configured to control a DC power supplied from the power supply circuit based on a result of the determination by the state determiner, and the state determiner determines, when a value obtained by subtracting the detection voltage from a first reference voltage is equal to or larger than a first threshold value, that the light source is in the turned-off state.