A light source device includes a light source that generates incoherent light, and an optical amplifier having gain characteristics indicating a gain at each wavelength, which receives the incoherent light output by the light source as input light, and outputs amplified light obtained by amplifying the input light, and a central wavelength of an intensity distribution indicating an intensity at each wavelength of the input light is a wavelength longer than a central wavelength of the gain characteristics indicating a gain at each wavelength of the optical amplifier.