A light source device includes a light source unit with at least one set of light sources, wherein each of the at least one set of light sources emits a light of a predetermined wavelength band; an optical waveguide unit that multiplexes light from the at least one set of light sources; and an incident unit, wherein on an incident surface of the incident unit, with an optical axis on the incident unit as a reference position, an installation state of each light source is adjusted such that the maximum separation distances are set equal to each other from the reference position to a maximum incident angle of an incident position of the respective light from the at least one set of light sources incident on the incident unit.