An image reading apparatus, including a driving unit, a separator unit, a conveyer unit, a reader unit, a reducer unit, a size detecting unit; and a controller is provided. The separator unit includes a drive shaft, a contact member, and a clutch. The controller manipulates the conveyer unit via the driving unit to convey the sheet at a first conveying speed when the size of the sheet detected by the size detecting unit is greater than a predetermined size. The controller manipulates the conveyer unit via the driving unit to convey the sheet at a second conveying speed, which is lower than the first conveying speed, when the size of the sheet detected by the size detecting unit is one of smaller than and equivalent to the predetermined size.