An image reading apparatus capable of determining whether or not to perform an inclination correction for an original to be read is provided. The image reading apparatus comprises a pair of guide plates to sandwich an end of the original in a width direction, an original guide width detection sensor for measuring a width between the guide plates with the original sandwiched, various rollers for conveying the original, and a surface reading unit for reading an image of the original. The image reading apparatus further comprises an image processing part which detects the width of the original being conveyed as an original width to detect an amount of inclination of the original being conveyed. Further, the image processing part corrects the image of the original read in accordance with the amount of inclination detected. The image reading apparatus compares the guide width with the original width and controls whether or not to perform the inclination correction in accordance with a result of the comparison.