An image scanner, in one of a system in which reading of data is performed by shifting a case with an image sensor incorporated therein relative to the surface of a fixed original, is disclosed comprising a window provided on the case for enabling the operator to make visual observation of data being read. The window is provided put therein with a member of frosted glass or the like capable of forming an image thereon, whereby the image of the data being read is adapted to be formed on this member.