Light projection unit, image reading device including same, and image forming apparatus including the image reading device

A light projection unit, comprising:

• a substrate;
• a plurality of light emitting elements arrayed on the substrate in a main scanning direction, each of the light emitting elements including a light emitting surface to project light;
• a light guide disposed facing the light emitting surfaces of the light emitting elements, to direct light projected from the light emitting elements onto an illumination area of an illumination target, the light guide including a first positioning portion;
• and
• a holder including a second positioning portion to engage the first positioning portion of the light guide, to position the light guide on the holder,
• the first positioning portion of the light guide being positioned between centers of light emission of adjacent light emitting elements in the main scanning direction of the substrate when the first positioning portion engages the second positioning portion of the holder, the first positioning portion includes a projection, and the second positioning portion includes a concave portion.