We report a novel ferroelectricity arise from the polar ordering of Fe 3+ and Fe2+ in a mixed valence triangular lattice oxide LuFe2O4, where the electric polarization do not arise from the ionic displacement. The polar ordering of Fe3+ and Fe 2+ was confirmed with a resonant X-ray scattering study in SPring-8. The origin of such ordering is the competitive interaction between Fe 3+ and Fe2+ in the triangular lattice, i.e. the charge frustration. The polar superlattice of Fe3+ and Fe2+ develops below 350K where the electric polarization appears. The ferroelectricity arising from the polar charge ordering or the polar electron distribution may have a great potential for the future application of ferroelectrics.