An image scanning device and a shading compensation method include reading out a second region of a reference white sheet spaced by a predetermined distance from a white roller prior to reading out a to-be-scanned document to generate a reference shading compensation value; comparing the generated reference shading compensation value and a stored initial sheet shading compensation value for the second region to calculate a final shading compensation value of a first region of the white roller; and compensating for image data of the read document according to the calculated final shading compensation value. Accordingly, the present invention generates a shading profile and compensates for shading distortions according to characteristic changes of an image readout unit, such as a CIS, thereby enabling more precise image data to be obtained.