The present invention relates to an image reading apparatus comprising a conveying means for conveying a sheet to a reading position; a platen glass guiding the sheet conveyed at the reading position; a reading apparatus for reading through the platen glass an image on the sheet conveyed at the reading position; a sheet guide member disposed on a side opposite to the reading device with respect to the platen glass for forming a small gap with the platen glass; and a driving means for moving the reading device. The drive device can move the reading device to a main reading position for reading operation at a position at which the sheet conveyed to the reading position is in contact with the platen glass and to at least one sub reading position for reading operation at a position at which the sheet conveyed to the reading position is not in contact with the platen glass.