  It has been known that, in the focus point scenario of supersymmetry, the
thermal relic of the lightest superparticle (LSP) is known to be a good
candidate of the cold dark matter. Assuming that the LSP in the focus-point
scenario be the cold dark matter, we address a question how and how well the
relic density of the LSP can be determined once the superparticles are found at
future e^+e^- linear collider. We will see that the determinations of the mass
of the LSP as well as those of the Higgsino-like chargino and neutralinos,
which will be possible by a study of the decay kinematics of the chargino or by
threshold scan, will give us important information to theoretically reconstruct
the relic density. Even if the Higgsino-like superparticles and the LSP are the
only superparticles which are kinematically accessible, relic density of the
LSP may be calculated with the accuracy of factor \sim 2; by adopting a mild
theoretical assumption or by determining the masses of the Wino-like
superparticles, uncertaintiy can be reduced to \sim 10 % or smaller.
