Toroidal nonneutral plasmas confined on helical magnetic surfaces with a helical axis are experimentally studied for the first time. Variations in space potential φ_s and electron density n_e on closed helical magnetic surfaces are clearly observed similar to those of helical plasmas with plane axes in past experiments. The measured data in this experiment are compared with numerical results obtained from Poisson's equation applied to poloidal cross sections of Heliotron J.