  A mechanism of radiatively generating neutrino masses is implemented in an
SU(2)_L x U(1)_Y x SU(2)'_L x U(1)'_Y model, where the first and second
families respect SU(2)_L x U(1)_Y while SU(2)'_L x U(1)'_Y is specific for the
third family. The fourth neutrino, nu_s, that has a U(1)_Y x U(1)'_Y coupling
joins in the model to induce neutrino mixings by additional interactions with e
and mu. The phenomenologically consistent oscillation of nu_s - nu_e requires a
dominated coupling of nu_s to e.
