1. An image reading apparatus, comprising: a reading unit that reads an image of an original while conveying the original, a detection unit that, based on image data obtained by reading a white image with the reading unit, detects an abnormal pixel based on a foreign substance adhering to a reading position of the original and outputs data indicating a position of the abnormal pixel, a correction unit that, based on the data outputted from the detection unit, corrects image data obtained by reading an original with the reading unit, and a control unit that performs control so that detection of the abnormal pixel by the detection unit is carried out immediately prior to reading of a first original, and a correction process by the correction unit based on the data indicating a position of the abnormal pixel is carried out on image data obtained by reading a second original following on from the first original.