  We propose a new scenario to produce the superheavy dark matter based on the
inflationary universe. In our scenario, the inflaton couples to both a boson
and a stable fermion. Although the fermion is produced by the inflaton decay
after inflation, almost energy density of the inflaton is transmitted into the
radiation by parametric resonance which causes the explosively copious
production of the boson. We show that the fermion produced by the inflaton
decay can be the superheavy dark matter, whose abundance in the present
universe coincides with the critical density. We also present two explicit
models as examples in which our scenario can be realized. One is the softly
broken supersymmetric theory. The other is the ``singlet majoron model'' with
an assumed neutrino mass matrix. The latter example can simultaneously explain
the neutrino oscillation data and the observed baryon asymmetry in the present
universe through the leptogenesis scenario.
