LIGHT SOURCE DEVICE

A light source device (1) includes a plurality of LEDs (3), a collimating optical system (5) disposed corresponding to the plurality of LEDs (3), a condensing optical system (7) that condenses light exiting from the collimating optical system (5), and a fly-eye integrator (10) into which the light exiting from the condensing optical system (7) is incident. Assuming that parallel light is defined as a virtual secondary light source (VS1), the parallel light being obtained from light traveling from a virtual primary light source (VS1) disposed at a back focus position of the condensing optical system (7) toward the condensing optical system (7) with a maximum effective acceptance angle (θL) of the fly-eye integrator (10) as a divergence angle and then passing through the condensing optical system (7), the virtual secondary light source (VS2) has a width that substantially coincides with a width of a secondary light source determined according to a shape of a light exit surface of the collimating optical system (5).