An image reader includes a first image reading unit that reads a first image on a first side of a sheet to output a first analog signal corresponding to the first image, a second image reading unit that reads a second image on a second side of the sheet, converts a second analog signal corresponding to the second image into a second digital signal, and outputs the second digital signal, a processor that processes the first analog signal and the second digital signal and includes a first converter converting the first analog signal into a first digital signal, and a timing signal output unit outputting, to the second image reading unit, a timing signal corresponding to a conversion time of the conversion by the first converter. Based on the timing signal, the second image reading unit outputs the second digital signal at a time outside the conversion time.