We study the pseudogap behaviour of atomic Fermi gases in the
BCS-BEC crossover. Including paring fluctuations, we calculate the
fermionic density of states above the superfluid transition temperature Tc, based on the fluctuation theory first developed by Nozieres and
Schmitt-Rink. We show that the pseudogap structure appears in the density of states above Tc in the crossover region, and it evolves as the
attractive interaction strength increases. We calculate the temperature dependence of the pseudogap energy, which vanishes as the
temperature rises, and determine the pseudogap region in the BCS-BEC phase diagram. We try to clarify the physics of the pseudogap by
examining the behaviour of the single-particle spectral density and self-energy.