The presence of approximate electron number conservation and $\ensuremath{\mu}\ensuremath{-}\ensuremath{\tau}$ permutation symmetry of ${S}_{2}$ is shown to naturally provide bilarge neutrino mixing. First, the bimaximal neutrino mixing together with ${U}_{e3}=0$ is guaranteed to appear owing to ${S}_{2},$ and then, the bilarge neutrino mixing together with $|{U}_{e3}|\ensuremath{\ll}1$ arises as a result of a tiny violation of ${S}_{2}.$ The observed mass hierarchy of $\ensuremath{\Delta}{m}_{\ensuremath{\bigodot}}^{2}$ $\ensuremath{\ll}$ $\ensuremath{\Delta}{m}_{\mathrm{atm}}^{2}$ is subject to another tiny violation of the electron number conservation. This scenario is realized in a specific model based on ${\mathrm{SU}(3)}_{L}\ifmmode\times\else\texttimes\fi{}{U(1)}_{N}$ with two-loop radiative mechanism for neutrino masses. The radiative effects from heavy leptons contained in lepton triplets generate the bimaximal structure, and those from charged leptons, which break ${S}_{2},$ generate the bilarge structure together with $|{U}_{e3}|\ensuremath{\ll}1.$ To suppress dangerous flavor-changing neutral current interactions due to Higgs exchanges especially for quarks, this ${S}_{2}$ symmetry is extended to a discrete ${Z}_{8}$ symmetry, which also ensures the absence of a one-loop radiative mechanism.