  Phenomena of neutrino oscillations are discussed on the basis of two-loop
radiative neutrino mechanism. Neutrino mixings are experimentally suggested to
be maximal in both atmospheric and solar neutrino oscillations. By using $L_e -
L_\mu - L_\tau$ ($\equiv L^\prime$)-conservation, which, however, only ensures
the maximal solar neutrino mixing, we find that two-loop radiative mechanism
dynamically generates the maximal atmospheric neutrino mixing and that the
estimate of $\Delta m^2_\odot/\Delta m^2_{atm} \sim\epsilon m_e/m_\tau$
explains $\Delta m^2_\odot/\Delta m^2_{atm} \ll 1$ because of $m_e/m_\tau \ll
1$, where $\epsilon$ measures the breaking of the $L^\prime$-conservation.
Together with $\Delta m^2_{atm} \approx 3\times 10^{-3}$ eV$^2$, this estimate
yields $\Delta m^2_\odot \sim 10^{-7}$ eV$^2$ for $\epsilon \sim 0.1$, which
corresponds to the LOW solution to the solar neutrino problem. Neutrino mass
scale is given by $(16\pi^2)^{-2} m_em_\tau /M$ ($M \sim$ 1 TeV), which is of
order 0.01 eV.
