The modification of gravity leads to the emergence of new degrees of freedom described by the dynamical field,
which can play a role of the dark energy and cause the late-time accelerated expansion of the Universe.
Besides the dark energy problem, it has been suggested that the new particle derived from the modified gravity can be a dark matter candidate.
Recently, we investigated the above scenario in the $F(R)$ gravity.
The $F(R)$ gravity includes the extra scalar field in addition to the graviton.
Since this scalar field originates from the gravitational theory,
it has very weak interactions with the standard model particles.
Moreover, the scalar field becomes heavy in the high-density region because of the chameleon mechanism.
These two properties suggest that the scalar field can be the cold dark matter.
We discuss the nature of this scalar field in the framework of particle physics and evaluate the lifetime of the new scalar particle.