An image scanning apparatus comprises a pair of regulating members that regulates a position of the document sheet stacked on a stacking unit, at least one of the regulating members being movable in a width direction; and units that detects a length in the width direction between the regulating members, and detects the width of the document sheet conveyed by a conveyance unit; wherein in a case where a difference between the detected length and the detected width of a document sheet is smaller than a threshold, a first sheet-to-sheet interval is set, and in a case where the difference between the detected length and the detected width of the document sheet is larger than the threshold, a second sheet-to-sheet interval which is larger than the first sheet-to-sheet interval is set.