  We show a TeV-scale seesaw model where Majorana neutrino masses, the dark
matter mass, and stability of the dark matter can be all originated from the
U(1)_{B-L} gauge symmetry. Dirac mass terms for neutrinos are forbidden at the
tree level by U(1)_{B-L}, and they are induced at the one-loop level by
spontaneous U(1)_{B-L} breaking. The right-handed neutrinos can be naturally at
the TeV-scale or below because of the induced Dirac mass terms with loop
suppression. Such right-handed neutrinos would be discovered at the CERN Large
Hadron Collider (LHC). On the other hand, stability of the dark matter is
guaranteed without introducing an additional Z_2 symmetry by a remaining global
U(1) symmetry after the U(1)_{B-L} breaking. A Dirac fermion Psi_1 or a complex
neutral scalar s^0_1 is the dark matter candidate in this model. Since the dark
matter (Psi_1 or s^0_1) has its own B-L charge, the invisible decay of the
U(1)_{B-L} gauge boson Z' is enhanced. Experimental constraints on the model
are considered, and the collider phenomenology at the LHC as well as future
linear colliders is discussed briefly.
