The present invention provides a light source device for emitting concentrated light, which is prepared by concentrating light emitted from a light source, including: the light source; a reflective box in which the light source is provided; a plurality of light guides having a circular column shape or a polygonal column shape and having two end surfaces being different in area; and light separating means, the reflective box having a plurality of openings, each opening being provided with one of the light guides in such a way that the end surface smaller in area faces the light source, and each light separating means being provided at a position between the adjacent ones of the openings. With this, a small-sized light source device for emitting light with high output and high directivity, and a simulated solar light irradiation device including the same are provided.