PROBLEM TO BE SOLVED: To provide a light source device capable of sweeping a wavelength to a short wavelength suitable for an OCT device for an eyeground at a high speed.SOLUTION: A light source device capable of changing an oscillation wavelength comprises an optical amplification medium for amplifying lights, and an optical resonator. The optical resonator has a first reflection member positioned on one side of the optical amplification medium, and second and third reflection members positioned on the other side of the optical amplification medium. The second and third reflection members reflect a flux of lights amplified by the optical amplification medium in a direction of the optical amplification medium while it is spatially separated in a radial direction of the flux of lights. The light source device changes the oscillation wavelength by changing an optical path length difference between a first optical path defined to include the first reflection member, the optical amplification medium, and the second reflection member, and a second optical path defined to include the first reflection member, the optical amplification medium, and the third reflection member, with an optical path length difference adjusting member capable of changing the optical path length difference.
