An image reading apparatus for reading the image surface of a sheet material brought into close contact with the image reading surface of an image reading unit while passing the sheet material through an image reading gap formed between the sheet conveying surface of a sheet conveying guide and the image reading surface, including a holding member for holding the image reading unit for movement in a direction to change the width of the image reading gap, an upstream roller pair having a first roller member displaceable in accordance with the thickness of the sheet material, and for nipping and conveying the sheet material into the image reading gap, and a downstream roller pair having a second roller member displaceable in accordance with the thickness of the sheet material, and for nipping and conveying the sheet material out of the image reading gap, wherein the image reading unit changes the width of the image reading gap on the basis of the displacement of at least one of the first roller member and the second roller member.