An image reading device comprises: a light source; a first optical element that focuses light emitted from the light source, the emitted light being reflected by a medium in a first detection area; a first detector that outputs first detection information in response to arrival of light in the first detection area; a second optical element that guides to a second detection area a portion of the light emitted from the light source, which portion does not arrive at the reflective medium in the first detection area; a second detector that outputs second detection information responsive to detection of light at the second detection area; and a generator that generates image data of the medium by revising the first detection information on the basis of the second detection information.