  We conducted $^{77}$Se-nuclear magnetic resonance studies of the iron-based
superconductor FeSe in magnetic fields of 0.6 to 19 T to investigate the
superconducting and normal-state properties. The nuclear spin-lattice
relaxation rate divided by the temperature $(T_1T)^{-1}$ increases below the
structural transition temperature $T_\mathrm{s}$ but starts to be suppressed
below $T^*$, well above the superconducting transition temperature
$T_\mathrm{c}(H)$, resulting in a broad maximum of $(T_1T)^{-1}$ at
$T_\mathrm{p}(H)$. This is similar to the pseudogap behavior in optimally doped
cuprate superconductors. Because $T^*$ and $T_\mathrm{p}(H)$ decrease in the
same manner as $T_\mathrm{c}(H)$ with increasing $H$, the pseudogap behavior in
FeSe is ascribed to superconducting fluctuations, which presumably originate
from the theoretically predicted preformed pair above $T_\mathrm{c}(H)$.
