An illuminator includes a concave mirror to reflect incident light in a predetermined direction, an inner reflective mirror provided on an optical axis of the concave mirror and having a reflective surface at least one surface thereof, a light source installed on at least one surface of the inner reflective mirror to generate and illuminate light, and a retro-reflective mirror provided at a focal point of the light reflected from the concave mirror, or in a vicinity of the focal point, and having an aperture through which some of the light illuminated from the light source and reflected by the concave mirror passes and a retro-reflective surface to reflect remaining light not passing through the aperture back toward the concave mirror.