8. The image scanning apparatus according to claim 2 , wherein, if the stripe pattern is detected in the image data on the last page of the document, the control unit compares the position in a primary scanning direction of the stripe pattern in the image data on a page of the document, which is scanned before the last page of the document, with the position in the primary scanning direction of the stripe pattern in the image data on the last page of the document to cause the display unit to display a guidance image prompting a user to clean the scanning face if a difference in position between the stripe patterns is over a predetermined threshold value.
2. The image scanning apparatus according to claim 1 , wherein the foreign object detecting unit detects a stripe pattern that extends in a scanning direction in the image data on the page of the document scanned by the image scanning unit to detect whether a foreign object exists on the scanning unit.