To assure a numerical aperture larger than the light distribution characteristic of a light source and to enable uniform and bright illumination.

The collector lens of the illumination device composed of a light source 1, a collector lens for converting approximately the light emitted from the light source 1 to parallel the luminous fluxes and a relay lens for transmitting approximately the parallel luminous fluxes thereof to an objective lens is composed of a positive first group G1 and a negative second group G2 and includes at least one aspherical optical element. The working distance WD of the collector lens satisfies 0.5<WD/f<1.5. In this equation, WD is the distance from the center of the light source to the apex of the surface on the extreme light source side of the collector lens and (f) is the focal length of the collector lens.