  Although it is usually thought that a class of weakly interacting massive
particle (WIMP) dark matters (DMs), which have the vector coupling with the $Z$
boson, is denied by null results of the direct DM searches, such WIMP DMs are
still viable if they are superheavy with the mass of $m_{DM} \gtrsim 10^9$ GeV.
In the future, the superheavy WIMP DMs can be searched up to $m_{DM} \simeq
10^{12}$ GeV, which corresponds to the so-called neutrino floor limit. We show
that the observed abundance of $\Omega_\mathrm{DM}h^2 \simeq 0.1$ for a
superheavy WIMP DM can be reproduced by a suitable reheating temperature of
$T_R \simeq m_{DM}/29$ after inflation, if the direct inflaton decay into DM is
negligible or kinematically forbidden.
