A light source device includes: light sources arranged in a plane; collimator lenses disposed in the vicinities of corresponding each of the light sources, each of the collimator lenses collimating a light beam emitted from the corresponding light source, and a holder that holds the light sources and the collimator lenses. The holder holds the light sources and the collimator lenses so that optical axes of the collimator lenses are respectively shifted parallel to optical axes of the light sources by shift lengths that are set so that light beams emitted from the light sources via the collimator lenses are focused on a certain region of an illumination subject body. The light beams emitted from the light sources are refracted by the collimator lenses and focused on the certain region.