An image reader, detachably attached to an electronic apparatus, for functionally expanding the electronic apparatus and for reading an image on a medium, includes an interface connectible to and disconnectible from the electronic apparatus a housing having an image-reading surface that faces the medium, a medium detecting part, provided on the image-reading surface, for detecting the medium, and an image reading part, provided on the image-reading surface and driven based on a detection result by the medium detecting part, for reading the image on the medium.