  We consider the minimal supersymmetric standard model (MSSM) extended by
introducing three right-handed (s)neutrinos to account for neutrino masses in
the oscillation experiments. Assuming that the neutrino masses are purely
Dirac-type, the lightest right-handed sneutrino $\tilde \nu_R$ can be the
lightest superparticle (LSP), which is a good candidate of cold dark matter
(CDM) of the universe. We study the possibility of realizing $\tilde
\nu_R$-CDM, paying a special attention to the production of $\tilde \nu_R$ via
decay of the next-to-lightest superparticle (NLSP) after its freeze-out time.
It is shown that the late decay of the MSSM-LSP (the LSP among superparticles
in the MSSM) can produce a sufficient amount of $\tilde \nu_R$ to explain the
observed dark-matter density, and that the $\tilde \nu_R$-CDM scenario can be
realized in a wide range of parameter space. We also consider the constraint on
the decay of MSSM-LSP from the big-bang nucleosynthesis (BBN); we found that
the case with stau being the MSSM-LSP is severely constrained.
