An image scanning device includes a scanning specifying unit, at least two document detecting units, a supply timing adjusting unit, and a document supplying unit. The scanning specifying unit specifies one of at least two scanning methods each having a different transportation interval between documents. The document detecting units are at least two in number and arranged to detect a document at different positions on a transportation route. The supply timing adjusting unit is arranged to measure a transportation distance of the document after detection by the document detecting units and to generate a supply signal. The document supplying unit is arranged to supply a document from a paper feed tray based on the supply signal. The supply timing adjusting unit is arranged to generate the supply signal based on a result of detection by the document detecting unit that corresponds to the specified scanning method.