An image reading device comprising: a document holding surface configured to hold a first document for flatbed scanning; a document conveyor unit configured to convey a second document along a conveying path for ADF-type image scanning including a curved path, the document conveyor unit including a conveyor roller configured to reverse a document conveying direction of the second document in the curved path; a first document contact surface configured to come into contact with a first side of the second document when the document conveyor unit conveys the second document; a second document contact surface configured to come into contact with a second side of the second document when the document conveyor unit conveys the second document; a first reading unit configured to: read an image on a side of the first document held by the document holding surface while traversing the first reading unit below the document holding surface; and read an image on the first side of the second document being conveyed by the document conveyor unit while the first reading unit is stationary below the first document contact surface; and a second reading unit disposed above the second document contact surface and configured to read an image on the second side of the second document being conveyed by the document conveyor unit, wherein at least a part of the conveyor roller is disposed lower than the document holding surface in a height direction of the image reading device that is perpendicular to a direction that the document holding surface extends. a document holding surface configured to hold a first document for flatbed scanning; a document conveyor unit configured to convey a second document along a conveying path for ADF-type image scanning including a curved path, the document conveyor unit including a conveyor roller configured to reverse a document conveying direction of the second document in the curved path; a first document contact surface configured to come into contact with a first side of the second document when the document conveyor unit conveys the second document; a second document contact surface configured to come into contact with a second side of the second document when the document conveyor unit conveys the second document; a first reading unit configured to: read an image on a side of the first document held by the document holding surface while traversing the first reading unit below the document holding surface; and read an image on the first side of the second document being conveyed by the document conveyor unit while the first reading unit is stationary below the first document contact surface; and read an image on a side of the first document held by the document holding surface while traversing the first reading unit below the document holding surface; and read an image on the first side of the second document being conveyed by the document conveyor unit while the first reading unit is stationary below the first document contact surface; and a second reading unit disposed above the second document contact surface and configured to read an image on the second side of the second document being conveyed by the document conveyor unit,