To provide a light source device that uses a light emitting diode and, at the same time, improves efficiency in the use of light at a low cost and to provide a projection lighting system.

The light source device 4 has: the light emitting diode LED 1, a parabolic mirror 2 disposed at the outgoing side of the light emitting diode LED 1, a uniformizing element 3 which uniformizes intensity distribution within the cross-section of a flux of light beams reflected by the parabolic mirror 2. The light emitting part 1a of the light emitting diode LED 1 is disposed at the focal point of the parabolic mirror 2. A flux of diverging light beams emitted from the light emitting diode 1 is reflected by the parabolic mirror 2 as a flux of substantially parallel light beams and thrown, via the uniformizing element 3 and a lighting optical system 5, onto a surface to be illuminated.