  A layered iron oxide \rfeo ($R$: rare-earth elements) is an exotic dielectric
material with charge-order (CO) driven electric polarization and
magnetoelectric effect caused by spin-charge coupling. In this paper, a theory
of electronic structure and dielectric property in \rfeo is presented. Charge
frustration in paired-triangular lattices allows a charge imbalance without
inversion symmetry. Spin frustration induces reinforcement of this polar CO by
a magnetic ordering. We also analyze an orbital model for the Fe ion which does
not show a conventional long-range order.
