  We propose a new scenario where neutrino masses are generated via operators
with the mass dimension higher than five, which are induced at the loop level.
The scenario is demonstrated with concrete models where neutrino masses are
generated via a one-loop dimension-seven operator which is induced through TeV
scale dynamics under the exact $Z_{2}$ symmetry. Tiny neutrino masses are
naturally induced from the TeV scale dynamics without introducing any
artificial assumption on magnitudes of coupling constants. The combination of
one-loop factor $1/(4\pi)^2$ and the factor of the ratio $(v/\Lambda)^2$
between the electroweak scale $v$ and new physics scale $\Lambda$ provides
sufficient suppression as compared to the model based on the dimension-five
operator induced at the tree level. The reproduction of the data for neutrino
masses and mixings are discussed under the constraint from experiments for
lepton flavour violation. We also mention phenomenological implications at
collider experiments and dark matter candidates.
