An illumination system that makes it possible to generate light with less color irregularity with a simple structure while restraining the increase of size is provided. A tube-shaped reflector having a tube-shaped wall whose inner surface is reflective is provided. The wall includes an aperture extending along a longitudinal axis of the reflector. In the reflector, plural sets of LEDs are arranged, where colors of light to be emitted from the LEDs in each set are different (for example, red, green, or blue LEDs are used for each set). The LEDs in each set are arranged along the longitudinal axis of the reflector to form a linear light source. A collecting lens is fixed to the reflector in such a way as to fill the aperture of the reflector.