1.  Field of the Invention
The present invention relates to an illumination apparatus, an image sensor unit, an image reading apparatus, and an image forming apparatus. 
2.  Description of the Related Art
Some illumination apparatuses that are used in image sensor units have a configuration in which a point light source is converted into a line light source through a rod-like light guide.  A light guide that is applied in such an illumination apparatus is generally made of a resin material such as an acrylic resin and is formed by injection molding.  A gate portion (sprue portion), which serves as an inflow port for a resin material when performing injection molding, is cut (gate cut) with hot nippers or the like after the injection molding to thereby detach the light guide.  In this configuration, projections and recesses may be caused by the cutting on the gate-cut surface (cut surface at the gate portion).  In such case, the optical properties may become unstable at the projections and recesses and leak light may arise from the projections and recesses, resulting in an uneven luminance distribution of the illumination light. 
Consequently, a configuration has been proposed in which a gate portion is provided at a location away from a portion that emits light to an object of illumination.  For example, Patent Document 1 discloses a configuration in which a light source is provided at one end of a light guide in an illumination apparatus, and a gate portion for injection molding is provided at the other end. 
In this connection, there is a demand to increase the light quantity of an illumination apparatus to improve the reading speed of the image sensor unit.  A common method to increase the light quantity of an illumination apparatus is to provide light sources at opposite ends of a light guide.  However, according to the configuration described in Patent Document 1, since a gate portion is provided at the other end face in the longitudinal direction, the problem is that the necessity arises to smoothen projections and recesses that arise on the gate-cut surface by grinding or the like, which leads to an increase in the production costs.     Patent Document 1: Japanese Laid-open Patent Publication No.  10-126581