The invention provides an image reading apparatus and method capable of performing skew error correction at high speed. In an image reading apparatus that conveys a stacked medium along a conveyance path, reads an image of the medium being conveyed, and discharges the medium after reading the image, the apparatus comprises calculation means for calculating the amount of skew of the medium while being conveyed, and correction means for correcting the amount of skew of the medium in accordance with the amount of skew calculated by the calculation means. The correction means comprise determination means for determining whether correction for the amount of skew should be performed or not, and control means for correcting the amount of skew of the medium. The calculation means comprise medium detection means for detecting the state of the medium conveyed along the conveyance path, and calculate the amount of skew from the detected result of the state of the medium. The control means comprise correction control means for correcting the amount of skew based on the amount of skew of the medium calculated by the calculation means when the determination means determine to correct the amount of skew. The calculation means comprise image reading means for reading an image of the medium conveyed along the conveyance path at a position closer on the conveyance path to the discharging side than the medium detection means, and calculate the amount of skew from the image data of the medium read by the image reading means.