  We study a model with $U(1)$ gauged lepton number symmetry in which the
active neutrino masses are generated at two-loop level through the spontaneous
breaking of the lepton number symmetry. To cancel gauge anomalies some exotic
leptons are introduced that also play an important role in generating neutrino
masses and the lightest neutral one can be a dark matter candidate. We discuss
a phenomenology of the neutral fermion sector including dark matter, lepton
flavor violations, and an extra neutral gauge boson $Z'$ that can be tested by
$e^+ e^-$ collision at the International Linear Collider (ILC).
