  We study the right-handed neutrino (RHN) dark matter candidate in the minimal
U(1)_{B-L} gauge extension of the standard model. The U(1)_{B-L} gauge symmetry
offers three RHNs which can address the origin of the neutrino mass, the relic
dark matter, and the matter-antimatter asymmetry of the universe. The lightest
among the three is taken as the dark matter candidate, which is under the B-L
gauge interaction. We investigate various scenarios for this dark matter
candidate with the correct relic density by means of the freeze-out or
freeze-in mechanism. A viable RHN dark matter mass lies in a wide range
including keV to TeV scale. We emphasize the sub-electroweak scale light B-L
gauge boson case, and identify the parameter region motivated from the dark
matter physics, which can be tested with the planned experiments including the
CERN SHiP experiment.
