An image scanning device with a time authentication requesting function enables documents, not subject to be converted into e-documents, to be easily converted into e-documents at a later date, and reduces costs required for assigning a timestamp. When a user instructs an account book e-document temporary scan, an original is scanned and stored. An account book temporary file name is assigned to the scanned original, and stored in an account book temporary folder. When the user instructs an estimate e-document temporary scan or a purchase order e-document temporary scan, scanned data of the original is assigned with a file name and stored in a temporary folder of each document type. Documents not subject to be converted into e-documents are stored under the same format as the e-document, and a timestamp is assigned collectively to necessary documents at a later date. Accordingly, costs required for the timestamp can be reduced.