A CPU checks a detecting state of a document set sensor at a point when the trailing end of a document sheet is assumed to pass through a separating position at which the document sheet is separated by a separation roller, based on a document length determined based on a detecting output from an abutting sensor. If the document set sensor does not detect a document sheet, the CPU determines that the next document sheet is not present. If the document set sensor detects a document sheet, the CPU checks a detecting state of the document presence detecting sensor. If the document presence detecting sensor detects a document sheet, the CPU determines that the next document sheet is present.