Abstract: A slit exposure type illumination apparatus for use in copying machines comprising a reflector having a quadratic reflecting surface, a hollow cylindrical member, at least part of which has the property of reflecting infrared light and allowing visible light to pass through and which is disposed near the focal line of the reflector, and a linear light source which is disposed near or in conformity with the focal line of the reflector, within the hollow member, so as to cause infrared light emitted from the linear light source to return to the linear light source by the hollow member to save electric energy required for the linear light source.