The present invention is to provide an image scanner, for scanning a reflection document or a transmission document. The image scanner comprises a shell, a document window glass, a transmission document carrier, and an optical chassis. The shell has a groove on its upper surface. The document window glass is capable of connecting with the groove, for scanning the reflection document. The transmission document carrier is capable of connecting with the groove, for scanning the transmission document. The optical chassis is provided at a proper location, for retrieving the images of the reflection document and the transmission document and converting them to an electronic signal. Wherein, by placing the document window glass or transmission document carrier into the groove, the image scanner is capable of scanning the reflection document or transmission document, respectively.