A light source apparatus includes a discharge lamp including a light-emitting container having a cavity in which a discharge medium is enclosed, and a pair of electrodes disposed such that respective tip portions thereof oppose each other in the cavity, and a driving unit that supplies a driving current to the pair of electrodes. The driving current is generated by modulating amplitude of alternating current having a frequency not lower than 1 kHz and not higher than 10 GHz, such that a first section and a second section in which the amplitude is smaller than in the first section are alternately repeated.