An image reading device includes a conveying unit, reading unit, and a control unit. The conveying unit conveys successive two sheets along a conveying path such that a gap is formed between the successive two sheets. The reading unit reads a sheet conveyed at a reading position in the conveying path. The reading unit has a light source and light-receiving unit. The control unit controls the light source to emit light at a first light intensity for a sheet that has reached the reading position. The light-receiving unit receives light reflected by the sheet present at the reading position. The control unit further controls the light source to emit a light at a second light intensity lower than the first light intensity during a period of time from when the reading unit has been read the preceding sheet to when the reading unit begins reading the subsequent sheet.