At a conventional image scanning method, it takes long time to transfer an image data of whole image, consequently it takes long time to display the whole image on a display. Therefore, an image scanning method and an apparatus thereof, with which a user can recognize mistakes at reading a document at earlier time, are provided. By one time scanning, an image data whose resolution is lower than fundamental resolution is read. The image data of lower resolution is obtained by that the image data are thinned out. And this image data having lower resolution is displayed on a display as a preview image. By rescanning, an image whose resolution is higher than the preview image is read and displayed. This preview image can be displayed in short time, therefore the user can recognize a mistake at earlier time.