A reflector array optical device has a plurality of dihedral corner reflector array optical elements which are disposed side by side on the same plane. Each of the dihedral corner reflector array optical elements has a substrate and a plurality of dihedral corner reflectors which each have at least two orthogonal side faces perpendicular to the principal surface of the substrate and orthogonal to each other, and which are formed on the substrate so that the orientations of the interior angles of the orthogonal side faces are aligned with each other.