An image reading device includes a first contact glass on which a document is conveyed from a document conveying part, a second contact glass on which the document is placed, a document separation member provided between the first contact glass and the second contact glass and separating the document from the first contact glass, a reading unit provided on rear-surface sides of the first contact glass and the second contact glass so as to be movable in a sub-scanning direction, and a guide member provided across both of the first contact glass and the document separation member on the rear-surface side of the first contact glass and guiding the movement of the reading unit.