A CS terminal receives a detection voltage VCS corresponding to voltage drop across a detection resistor RCS provided on a path of a drive current ILED or an inductor current IL. An ADIM terminal receives an analog dimming voltage VADIM indicating a target amount of the drive current ILED. A coefficient circuit multiplies at least one of the detection voltage VCS and the analog dimming voltage VADIM by a variable coefficient and generates a current detection signal IS and a current setting signal IREF. A pulse modulator generates a drive pulse SDRV whose duty ratio is adjusted such that the current detection signal IS approaches the current setting signal IREF. A driver drives a switching transistor M according to the drive pulse SDRV.