An image reading apparatus has a plurality of emitters that emit light onto a manuscript surface in a light quantity that is the synthesized light quantity of light emitted from the plurality of emitters. In the image reading apparatus, determination on the abnormality of a reference white data level value at the time of turning on a power supply is carried out through comparison between the reference white data level value with a predetermined absolute value. A normal reference white data level value is stored in a first storing unit, while a comparison white data level value detected at the time of manuscript reading operation is stored in a second storing unit. Then, a differential between the level values stored in the first and second storing units is calculated, and an abnormality determining unit compares the differential with a predetermined threshold to detect the abnormality of an emitter.