Provided is an image reading device including: a light source member including light source portions emitting light; a light guide member including: an input section to which the light emitted from the light source portions is input; and an output section from which the input light is output; a support member supporting the light source member and the light guide member and having higher rigidity than the light source member and the light guide member; a retaining member configured to press the light guide member toward the support member and configured to retain the light guide member in a supported state by the support member; and a protrusion-shaped contact section provided on the light guide member and contacting the retaining member, the contact section protruding in a direction perpendicular from the predetermined main scanning direction from the light guide member toward the retaining member.