In a lighting apparatus for an illumination light source (discharge lamp or the like), a fly-back type DC-DC converter circuit comprises a transformer and a switching element. A control circuit is provided for controlling power supplied to the illumination light source, such that operation is controlled in a current boundary mode by a control signal sent from the control circuit to the switching element. A fluctuation generator circuit is provided for giving fluctuations to a frequency at which the switching element is driven by changing the power supplied to the illumination light source with reference to a target power value associated with the power control for the illumination light source.