Patent ID: 8279502

Claim:
An image reading apparatus having a light source emitting light on a manuscript, a photoelectric conversion element detecting refection light from the manuscript to obtain an analog image signal, and a signal processing unit digitizing the analog image signal to output a digitized image signal, the image reading apparatus comprising: a plurality of LEDs as the light source disposed on both end sides in a main scanning direction that is a width direction of the manuscript; a light guide configured to synthesize incident light from the plurality of LEDs to emit the synthesized light as a band-shaped light flux onto the manuscript; a detecting unit configured to detect a white data level at a time of a manuscript reading operation at each position near the light source that is on the front end side and the rear end side in the main scanning direction; and an abnormality detecting unit configured to calculate a differential between two detected white data levels to detect abnormality of the light source from the differential, the two detected white data levels include a front reference white data level detected at the front end side in the main scanning direction, and a rear reference white data level detected at the rear end side in the main scanning direction.