  We consider dark matter physics in a model for the dark sector with extra
dark U(1)$_X$ gauge symmetry. The dark sector is composed of exotic fermions
that are charged under both dark U(1)$_X$ and the standard model SU(3)$_C
\times$U(1)$_Y$ gauge groups, as well as standard model singlet complex scalars
$\Phi$ and $X$ with nonzero U(1)$_X$ charge. In this model, there are two dark
matter candidates$-$a scalar and a fermion$-$both of which are stabilized by
accidental $Z_2$ symmetry. Their thermal relic density, and direct and indirect
detection constraints are discussed in detail and we search for the parameter
space of the model accommodating dark matter observations. We also discuss
constraints from diphoton resonance searches associated with the scalar field
which breaks the dark U(1)$_X$, in a way consistent with dark matter physics.
In addition, implications for collider physics are discussed, focusing on the
production cross section of the scalar boson.
