This image reading apparatus, includes: a first retaining member that retains a lens unit; a second retaining member that retains a sensor unit; and a positioning member that sets a relative position between the first retaining member and the second retaining member, wherein the positioning member comprises: a first concave portion that is sagged from a first contact surface to be in contact with the first retaining member; and a second concave portion that is sagged from a second contact surface to be in contact with the second retaining member, and the positioning member is fixed to the first retaining member and the second retaining member by an adhesive filled in the first concave portion and the second concave portion.