A control IC controls a switching power supply configured to supply a driving voltage Vout to one terminal of an LED string which is driven in an intermittent manner. A sample-and-hold circuit performs sampling of a detection voltage Vs that corresponds to a driving voltage Vout in the on period, and holds the sampled detection voltage Vs in the off period. In the off period, a pulse modulator generates a pulse signal having a duty ratio adjusted such that a hold detection voltage VsH output from the sample-and-hold circuit matches the detection voltage Vs. A driver drives a switching transistor according to the pulse signal.