A first image reading chip for reading an image of a first surface of a medium includes a first pixel portion that outputs a first pixel signal, a first output circuit that outputs a signal based on the first pixel signal, and a first output selection unit that selects a first drive capability as a drive capability of the first output circuit, and a second image reading chip for reading an image of a second surface of a medium includes a second pixel portion that outputs a second pixel signal, a second output circuit that outputs a signal based on the second pixel signal, and a second output selection unit that selects a second drive capability as a drive capability of the second output circuit.