The modified gravity theories have been investigated so far to explain the late-time accelerated expansion of the Universe.

The modification of gravity leads to the emergence of the new degree of freedom described by the dynamical field, which plays a role of the dark energy and causes the cosmic acceleration.

Besides the dark energy problem, it has been suggested that the new particle derived from the modified gravity can be a dark matter candidate.

In this talk, I discuss the above scenario in the F(R) gravity.

The F(R) gravity includes the extra scalar field, so-called scalaron, in addition to the graviton.

Since this scalar field originates from the gravitational theory, it has very weak interactions with the standard model particles.

And, 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.

I study the nature of this scalar field from the viewpoint of particle physics.