A light source device includes a plurality of light emitting parts, a first lens, and an optical lens. Each light emitting part is configured to emit light from the light emitting surface at a first full-width half-maximum and is configured to be individually turned on. The optical lens has a first surface including incident regions and a second surface including emission regions. A minimum distance between the first surface of the optical lens and the first lens is 0.1 mm or more and 1.0 mm or less. A light emitted from each of the light emitting parts enters the optical lens through the first lens, the light being emitted from the first lens at a second full-width half-maximum smaller than the first full-width half-maximum, such that lights emitted from two or more of the light emitting parts are irradiated to two or more corresponding irradiation regions.