An image reader is provided, which includes a first analog front end unit configured to perform A/D conversion for analog signals that are output via a first group of channels of a number resulting from rounding up, to a closest whole number, an average value between a number of at least one channel for a first image reading unit and a number of channels for a second image reading unit, among analog signals output from the first image reading unit and the second image reading unit, and a second analog front end unit configured to perform A/D conversion for analog signals that are output via a second group of channels other than the channels in the first group, among the analog signals output from the first image reading unit and the second image reading unit.