1. A method of correcting distortion caused by scanning, comprising the steps of: scanning an original in a main scanning direction and a sub scanning direction into scanned image data; determining whether any of a predetermined correction data set of a page outline, a rule line and a character line exists in the scanned image data; and correcting the distortion based upon the correction data set, the rule line and the character line being used alone or in combination if the page outline does not exist in the scanned image data.