A lighting device includes a switching regulator having an inductor and a switching device, and a controller. The controller includes a peak current detector that outputs a peak detection signal when detecting that a current flowing through the switching device reaches a threshold, a zero-cross detector that outputs a zero-cross detection signal when a current discharged from the inductor reaches a predetermined lower limit value or less, a synchronization signal controller that outputs a periodic synchronization signal, and a switching controller. The switching controller turns on the switching device in synchronization with a start of an on-period of the synchronization signal and the zero-cross detection signal, and turns off the switching device in synchronization with the peak detection signal. The peak current detector reduces the threshold when an on-period of the synchronization signal finishes, and increases the threshold to an original value when an on-period of the synchronization signal starts.