Image reading device and image forming apparatus including the same

An image reading device including a document feeding device, which has a document conveyance path from a sheet feeding port to a sheet discharge port via an upper surface side of an automatic reading glass and conveys a document set on a document placing part along the document conveyance path, a first reading unit for reading a document image of one surface of the document passing through a first reading position set at the upper surface side of the automatic reading glass in the document conveyance path from a lower surface side of the automatic reading glass, and an image data processing unit for converting the document image read by the first reading unit into image data and storing the image data, comprising:

• a first marking part provided at a downstream side in a document conveyance direction from the first reading position in the document conveyance path to apply a first predetermined mark to a margin of an upstream side in the document conveyance direction from an image formation region on the one surface of the document;
• and
• a first mark erasing part provided in the vicinity of the sheet discharge port of the document feeding device to erase the first predetermined mark applied to the margin of the document when the first predetermined mark passes through the sheet discharge port,
• wherein the image data processing unit is configured to determine whether the first predetermined mark exists in the image data of the document image of the one surface read by the first reading unit, and to erase the image data when it is determined that the first predetermined mark exists.