A light beam emitted from a light source (11) impinges on the spherical surface (20a) of a collimator lens (20) substantially perpendicularly thereto. A light beam making a small angle to the optical axis impinges on the ellipsoid (20c) and then it is refracted. The ellipsoid (20c) converts light beams diverging from a light source located at the first focal point thereof into parallel light beams. A light beam making a large angle to the optical axis impinges on an ellipsoid (20b) and then it is reflected totally off the ellipsoid (20b). A light beam diverging from a light source located at the first focal point of the ellipsoid (20b) is converted into a light beam being focused on the second focal point thereof. An ellipsoid (20d) converts the light beams focused on the second focal point thereof into parallel light beams. In this way, the light beams emitted from the light source (11) are converted into substantially parallel light beams by the collimator lens (20), thus providing an illuminator exhibiting high directivity, high efficiency and high uniformity in light quantity distribution.