An LED light source device installed in an image reading apparatus, includes an LED that is a light-emitting source; and a light guide for reflecting light of the LED by an inner surface thereof to diffuse along a main scanning line direction and irradiating the light reflected by the light guide to a surface of a sheet. The light guide has a plurality of reflecting surface bodies spaced at predetermined pitches in the main scanning line direction inside an inner surface reflection optical path to reflect the light from the LED toward an outside along the main scanning line direction. The plurality of reflecting surface bodies includes a first reflecting surface body and a second reflecting surface body, and a length in a perpendicular direction to the main scanning line direction of the second reflecting surface body is different from that of the first reflecting surface body.