  We propose a simple testable model with mass generation mechanisms for dark
matter and neutrino based on the gauged $U(1)_{B-L}$ symmetry and an exact
$Z_2$ parity. The $U(1)_{B-L}$ symmetry is spontaneously broken at the TeV
scale, by which $Z_2$-odd right-handed neutrinos receive Majorana masses of the
electroweak scale. The lightest one is a dark matter candidate, whose stability
is guaranteed by the $Z_2$ parity. Resulting lepton number violation is
transmitted to the left-handed neutrinos $\nu_L^i$ via the loop-induced
dimension-six operator. Consequently, the tiny masses of $\nu_L^i$ can be
generated without excessive fine tuning. The observed dark matter abundance can
be reproduced by the pair annihilation via the s-channel scalar exchange due to
mixing of neutral components of $\Phi$ and $S$, where $\Phi$ and $S$
respectively represent the Higgs doublet and the additional scalar singlet with
the $B-L$ charge. The model can be tested at collider experiments as well as
flavor experiments through the discriminative predictions such as two light
neutral Higgs bosons with large mixing, invisible decays of the Higgs bosons as
well as the $B-L$ gauge boson, and lepton flavor violation.
