  We propose an electroweakly interacting spin-1 dark matter (DM) model. The
electroweak gauge symmetry, SU(2)$_L\times$U(1)$_Y$, is extended into
SU(2)$_0\times$SU(2)$_1 \times $SU(2)$_2 \times$U(1)$_Y$. A discrete symmetry
exchanging SU(2)$_0$ and SU(2)$_2$ is imposed. This discrete symmetry
stabilizes the DM candidate. The spin-1 DM particle ($V^0)$ and its SU(2)$_L$
partners ($V^\pm$) interact with the Standard Model (SM) electroweak gauge
bosons without any suppression factors. Consequently, pairs of DM particles
efficiently annihilate into the SM particles in the early universe, and the
measured value of the DM energy density is easily realized by the thermal
freeze-out mechanism. The model also predicts a heavy vector triplet ($W'^\pm$
and $Z'$) in the visible sector. They contribute to the DM annihilation
processes. The mass ratio of $Z'$ and $V^0$ determines values of various
couplings, and constraints on $W'$ and $Z'$ restrict regions of the parameter
space that are viable for DM physics. We investigate the constraints from
perturbative unitarity of scalar and gauge couplings, the Higgs signal
strength, $W'$ search at the LHC, and DM direct detection experiments. It is
found that the relic abundance of $V^0$ explains the right amount of the DM
energy density for 3 TeV $\lesssim m_{V^0} \lesssim$ 19 TeV.
