The image reading apparatus is of the multi-chip line sensor having a plurality of photoelectric conversion elements connected through corresponding switching elements commonly to every one another. Each group of the commonly connected photoelectric conversion elements outputs on a common line an image signal which is then fed to a sample hold circuit and is thereafter outputted from a single output terminal. By such construction, the image signal from the photoelectric conversion elements is sequentially outputted externally from the single output terminal in the form of output waveshape as held in the sample hold circuit in such manner as to prolong output duration of each bit image signal to thereby enable fast operation of the line sensor.