An image reader comprising: a first image reading unit configured to read an image on a first side of a first document sheet being conveyed on a feeding path, and output an analog signal corresponding to the read image of the first side; a second image reading unit configured to read an image on a second side opposite to the first side of the first document sheet being conveyed on the feeding path, and output a digital signal corresponding to the read image of the second side in a differential transmission method; a processor configured to process the analog signal output from the first reading unit and the digital signal output from the second image reading unit; a base body; a document table fixed to the base body, the document table being configured such that a second document sheet can be placed thereon; a first harness configured to transmit, to the processor, the analog signal output from the first image reading unit: and a second harness configured to transmit, to the processor, the digital signal output from the second image reading unit; wherein the second image reading unit is provided to the base body, and configured to perform any one of: a first reading operation to read the image on the second side of the first document sheet being conveyed on the feeding path while statically staying in the base body; and a second reading operation to read an image on a single side of the second document sheet placed on the document table while moving in a predetermined direction along the document table, and wherein the second harness has a length that allow the second image reading unit to move in the predetermined direction along the document table. a first image reading unit configured to read an image on a first side of a first document sheet being conveyed on a feeding path, and output an analog signal corresponding to the read image of the first side; a second image reading unit configured to read an image on a second side opposite to the first side of the first document sheet being conveyed on the feeding path, and output a digital signal corresponding to the read image of the second side in a differential transmission method; a processor configured to process the analog signal output from the first reading unit and the digital signal output from the second image reading unit; a base body; a document table fixed to the base body, the document table being configured such that a second document sheet can be placed thereon; a first harness configured to transmit, to the processor, the analog signal output from the first image reading unit: and a second harness configured to transmit, to the processor, the digital signal output from the second image reading unit; wherein the second image reading unit is provided to the base body, and configured to perform any one of: a first reading operation to read the image on the second side of the first document sheet being conveyed on the feeding path while statically staying in the base body; and a second reading operation to read an image on a single side of the second document sheet placed on the document table while moving in a predetermined direction along the document table, and a first reading operation to read the image on the second side of the first document sheet being conveyed on the feeding path while statically staying in the base body; and a second reading operation to read an image on a single side of the second document sheet placed on the document table while moving in a predetermined direction along the document table, and wherein the second harness has a length that allow the second image reading unit to move in the predetermined direction along the document table.