  The possibility of the CDM axino is presented. From the early days of
supersymmetry, axino has been considered as hot dark matter and warm dark
matter. But the CDM axino has been considered quite recently. It is because the
low reheating temperature of the universe is gaining momentum recently from
various considerations in particle cosmology. I present a general introduction
on the CDM's, in particular the axino, the calculation on the axino density in
the universe, and the constraints imposed on the axino parameters.
