Disclosed are an illuminator and an image forming apparatus employing an illuminator. The illuminator includes a light guide to guide light generated from a light source to an object to be illuminated. The light guide includes at least one incidence face facing the light source and an emission face configured to emit the light to the target object. A diffusion pattern may be formed on the emission face to extend from one longitudinal end to the other longitudinal end of the emission face. The emission face may have a constant cross section or a varying cross section along a longitudinal direction thereof. The illuminator may be part of an image reading device to uniformly or near uniformly irradiate light to a document. The illuminator may also be incorporated in an image forming apparatus to irradiate light to a photosensitive body for elimination or reduction of electric potential from the photosensitive body.