Patent ID: 8335023

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 determining unit configured to determine whether a reference white data level value, which is obtained at a time of turning on a power supply to the apparatus, is smaller or larger than a first threshold value, which is predetermined based on a level that is obtainable as a result of normal switching on of all LEDs a first storing unit configured to store the reference white data level value, when the determining unit determines that the reference white data level value is larger than the first threshold value; a second storing unit configured to store a comparison white data level value detected at a time of a manuscript reading operation; a calculating unit configured to calculate a differential between the reference white data level value stored in the first storing unit and the comparison white data level value stored in the second storing unit; and an abnormality detecting unit configured to detect abnormality of the light source through comparison between the calculated differential and a predetermined second threshold value.