Abstract: An image reader (100) has a removable memory device (2) which stores authentication information for performing identity authentication of a user. An image reader body (1) has an authentication processing unit (6) performing the identity authentication to identify whether a user is the authorized person by checking authentication information (8) stored in the removable memory device (2) and registered authentication information (9) in advance in the image reader (100) with each other. Only when the authentication by the authentication processing unit (6) is successful, a document (3) is read by using the image reader (100), and a digital signature or approval information is added to image data (15) which has been read.