Abstract: A light source device for a fiber optic illumination system comprises a solid-state light emitting element having an emission surface shaped in quadrate, a light collection lens system with a positive power comprising at least a plano-convex lens, and a reflection member having a cylindrical reflection surface therein, all of which are arranged in this order coaxially with one another along a principal axis passing a center of the light emitting element, wherein the plano-convex lens is placed with a plane surface thereof directly facing and located at a space distance apart from the emission surface so as to form a virtual image of the emission surface.