A light source device for radiating a stimulated emission from a semiconductor laser to outside via a multiple scattering optical system, which system has a first region located adjacent to the semiconductor laser and a second region that abuts on the first region and reaches the outside. The first region contains scatterers at a higher density than the second region does. The light source device has an amount of near-field pattern speckles .sigma..sub.PAR of 3.times.10.sup.-3 or more. The second region may have a lens portion as a magnifier for at least a principle part of a secondary planar light source formed at an interface between the first and second regions.