The thermal inflation is the most plausible mechanism that solves the
cosmological moduli problem naturally. We discuss relic abundance of superheavy
particle X in the presence of the thermal inflation assuming that its
lifetime is longer than the age of the universe, and show that the long-lived
particle X of mass 1012--1014 GeV may form a part of the dark
matter in the present universe in a wide region of parameter space of the
thermal inflation model. The superheavy dark matter of mass ∼1013 GeV
may be interesting in particular, since its decay may account for the observed
ultra high-energy cosmic rays if the lifetime of the X particle is
sufficiently long.Comment: 13 pages (RevTex file) including 8 figures, revised version to be
published in Physical Review