US Patent 7630102 Image reading device and method

An image reading device reads out an image of a document being conveyed above one main surface of a contact glass, changes a document reading position if the image has an abnormality, and gives a warning if the changed document reading position is located at a predetermined reference position. The image reading device has a setting portion for changing the reference position in accordance with the number of documents that have passed the document reading position during the time when no abnormality in images is obtained by reading the documents.