An image reader includes a reading carriage, on which a reading unit is mounted and which performs scanning along a document-sheet platen in a scanning direction, and an annular belt that draws the reading carriage. The belt includes a first side extending in the scanning direction to which the reading carriage is fixed, and a second side that is disposed to be spaced from the first side. The detection unit that detects a document sheet mounted on the document-sheet platen is disposed in a region between the first side and the second side of the belt in a direction intersecting with the scanning direction.